Section 8-4
Solve Systems by Adding, Subtracting, and
    Multiplying (Linear Combinations)
Essential Questions
 How do you solve systems of equations
 by adding and subtracting?
 How do you solve systems of equations
 by adding and multiplying?


 Where you’ll see this:
  Landscaping, construction, sports
Why another method?
Why another method?
 Graphing: Problems with accuracy
Why another method?
 Graphing: Problems with accuracy
 Substitution: Need an isolated variable
Why another method?
 Graphing: Problems with accuracy
 Substitution: Need an isolated variable
 Combinations: Could speed up
 process
Why another method?
    Graphing: Problems with accuracy
    Substitution: Need an isolated variable
    Combinations: Could speed up
    process

Look at the system to determine best method
Solve by Combinations
Solve by Combinations
1. Choose a variable to eliminate (your choice).
Solve by Combinations
1. Choose a variable to eliminate (your choice).
2. Make the coefficients of that variable
   opposite. You might need to multiply to do
   this. Then combine equations.
Solve by Combinations
1. Choose a variable to eliminate (your choice).
2. Make the coefficients of that variable
   opposite. You might need to multiply to do
   this. Then combine equations.
3. Solve for the remaining variable.
Solve by Combinations
1. Choose a variable to eliminate (your choice).
2. Make the coefficients of that variable
   opposite. You might need to multiply to do
   this. Then combine equations.
3. Solve for the remaining variable.
4. Plug back into an original equation to find
   the other variable.
Solve by Combinations
1. Choose a variable to eliminate (your choice).
2. Make the coefficients of that variable
   opposite. You might need to multiply to do
   this. Then combine equations.
3. Solve for the remaining variable.
4. Plug back into an original equation to find
   the other variable.
5. Check and rewrite the answer.
Example 1
Solve by combining the equations
            −2x + 3 y = 2
            
         a. 
             2x + 7 y = 18
            
Example 1
       Solve by combining the equations
                    −2x + 3 y = 2
                    
                 a. 
                     2x + 7 y = 18
                    
−2x + 3 y = 2
Example 1
       Solve by combining the equations
                    −2x + 3 y = 2
                    
                 a. 
                     2x + 7 y = 18
                    
−2x + 3 y = 2
 2x + 7 y = 18
Example 1
       Solve by combining the equations
                    −2x + 3 y = 2
                    
                 a. 
                     2x + 7 y = 18
                    
−2x + 3 y = 2
 2x + 7 y = 18
Example 1
       Solve by combining the equations
                    −2x + 3 y = 2
                    
                 a. 
                     2x + 7 y = 18
                    
−2x + 3 y = 2
 2x + 7 y = 18
  10 y = 20
Example 1
        Solve by combining the equations
                    −2x + 3 y = 2
                    
                 a. 
                     2x + 7 y = 18
                    
−2x + 3 y = 2
 2x + 7 y = 18
  10 y = 20
   10    10
Example 1
       Solve by combining the equations
                    −2x + 3 y = 2
                    
                 a. 
                     2x + 7 y = 18
                    
−2x + 3 y = 2
 2x + 7 y = 18
  10 y = 20
   10 10
    y=2
Example 1
       Solve by combining the equations
                    −2x + 3 y = 2
                    
                 a. 
                     2x + 7 y = 18
                    
−2x + 3 y = 2
                 −2x + 3(2) = 2
 2x + 7 y = 18
  10 y = 20
   10 10
    y=2
Example 1
       Solve by combining the equations
                    −2x + 3 y = 2
                    
                 a. 
                     2x + 7 y = 18
                    
−2x + 3 y = 2
                 −2x + 3(2) = 2
 2x + 7 y = 18
                  −2x + 6 = 2
  10 y = 20
   10 10
    y=2
Example 1
       Solve by combining the equations
                    −2x + 3 y = 2
                    
                 a. 
                     2x + 7 y = 18
                    
−2x + 3 y = 2
                 −2x + 3(2) = 2
 2x + 7 y = 18
                  −2x + 6 = 2
  10 y = 20             −6 −6
   10 10
    y=2
Example 1
       Solve by combining the equations
                    −2x + 3 y = 2
                    
                 a. 
                     2x + 7 y = 18
                    
−2x + 3 y = 2
                 −2x + 3(2) = 2
 2x + 7 y = 18
                  −2x + 6 = 2
  10 y = 20             −6 −6
   10 10             −2x = −4
    y=2
Example 1
       Solve by combining the equations
                    −2x + 3 y = 2
                    
                 a. 
                     2x + 7 y = 18
                    
−2x + 3 y = 2
                 −2x + 3(2) = 2
 2x + 7 y = 18
                  −2x + 6 = 2
  10 y = 20             −6 −6
   10 10             −2x = −4
    y=2               −2     −2
Example 1
       Solve by combining the equations
                    −2x + 3 y = 2
                    
                 a. 
                     2x + 7 y = 18
                    
−2x + 3 y = 2
                 −2x + 3(2) = 2
 2x + 7 y = 18
                  −2x + 6 = 2
  10 y = 20             −6 −6
   10 10             −2x = −4
    y=2               −2 −2
                       x=2
Example 1
       Solve by combining the equations
                    −2x + 3 y = 2
                    
                 a. 
                     2x + 7 y = 18
                                     Check:
−2x + 3 y = 2
                 −2x + 3(2) = 2
 2x + 7 y = 18
                  −2x + 6 = 2
  10 y = 20             −6 −6
   10 10             −2x = −4
    y=2               −2 −2
                       x=2
Example 1
       Solve by combining the equations
                    −2x + 3 y = 2
                    
                 a. 
                     2x + 7 y = 18
                                        Check:
−2x + 3 y = 2                         −2(2) + 3(2) = 2
                 −2x + 3(2) = 2
 2x + 7 y = 18
                  −2x + 6 = 2
  10 y = 20             −6 −6
   10 10             −2x = −4
    y=2               −2 −2
                       x=2
Example 1
       Solve by combining the equations
                    −2x + 3 y = 2
                    
                 a. 
                     2x + 7 y = 18
                                        Check:
−2x + 3 y = 2                         −2(2) + 3(2) = 2
                 −2x + 3(2) = 2
 2x + 7 y = 18                          −4 + 6 = 2
                  −2x + 6 = 2
  10 y = 20             −6 −6
   10 10             −2x = −4
    y=2               −2 −2
                       x=2
Example 1
       Solve by combining the equations
                    −2x + 3 y = 2
                    
                 a. 
                     2x + 7 y = 18
                                        Check:
−2x + 3 y = 2                         −2(2) + 3(2) = 2
                 −2x + 3(2) = 2
 2x + 7 y = 18                          −4 + 6 = 2
                  −2x + 6 = 2
  10 y = 20             −6 −6         2(2) + 7(2) = 18
   10 10             −2x = −4
    y=2               −2 −2
                       x=2
Example 1
       Solve by combining the equations
                    −2x + 3 y = 2
                    
                 a. 
                     2x + 7 y = 18
                                        Check:
−2x + 3 y = 2                         −2(2) + 3(2) = 2
                 −2x + 3(2) = 2
 2x + 7 y = 18                          −4 + 6 = 2
                  −2x + 6 = 2
  10 y = 20             −6 −6         2(2) + 7(2) = 18
   10 10             −2x = −4           4 + 14 = 18
    y=2               −2 −2
                       x=2
Example 1
       Solve by combining the equations
                    −2x + 3 y = 2
                    
                 a. 
                     2x + 7 y = 18
                                        Check:
−2x + 3 y = 2                         −2(2) + 3(2) = 2
                 −2x + 3(2) = 2
 2x + 7 y = 18                          −4 + 6 = 2
                  −2x + 6 = 2
  10 y = 20             −6 −6         2(2) + 7(2) = 18
   10 10             −2x = −4           4 + 14 = 18
    y=2               −2 −2
                       x=2                (2, 2)
Example 1
Solve by combining the equations
            10x + 4 y = 14
            
         b. 
            x + 4 y = 5
            
Example 1
Solve by combining the equations
            10x + 4 y = 14
            
         b. 
             x + 4 y = 5)(−1)
            (
Example 1
       Solve by combining the equations
                     10x + 4 y = 14
                     
                  b. 
                      x + 4 y = 5)(−1)
                     (
10x + 4 y = 14
Example 1
        Solve by combining the equations
                      10x + 4 y = 14
                      
                   b. 
                       x + 4 y = 5)(−1)
                      (
10x + 4 y = 14
 − x − 4 y = −5
Example 1
        Solve by combining the equations
                      10x + 4 y = 14
                      
                   b. 
                       x + 4 y = 5)(−1)
                      (
10x + 4 y = 14
 − x − 4 y = −5
Example 1
        Solve by combining the equations
                      10x + 4 y = 14
                      
                   b. 
                       x + 4 y = 5)(−1)
                      (
10x + 4 y = 14
 − x − 4 y = −5
      9x = 9
Example 1
          Solve by combining the equations
                      10x + 4 y = 14
                      
                   b. 
                       x + 4 y = 5)(−1)
                      (
10x + 4 y = 14
 − x − 4 y = −5
      9x = 9
      9      9
Example 1
          Solve by combining the equations
                      10x + 4 y = 14
                      
                   b. 
                       x + 4 y = 5)(−1)
                      (
10x + 4 y = 14
 − x − 4 y = −5
      9x = 9
      9      9
     x=1
Example 1
          Solve by combining the equations
                      10x + 4 y = 14
                      
                   b. 
                       x + 4 y = 5)(−1)
                      (
10x + 4 y = 14
 − x − 4 y = −5       1+ 4 y = 5
      9x = 9
      9      9
     x=1
Example 1
          Solve by combining the equations
                      10x + 4 y = 14
                      
                   b. 
                       x + 4 y = 5)(−1)
                      (
10x + 4 y = 14
 − x − 4 y = −5       1+ 4 y = 5
      9x = 9         −1        −1
      9      9
     x=1
Example 1
          Solve by combining the equations
                      10x + 4 y = 14
                      
                   b. 
                       x + 4 y = 5)(−1)
                      (
10x + 4 y = 14
 − x − 4 y = −5       1+ 4 y = 5
      9x = 9         −1        −1
      9      9            4y = 4

     x=1
Example 1
          Solve by combining the equations
                      10x + 4 y = 14
                      
                   b. 
                       x + 4 y = 5)(−1)
                      (
10x + 4 y = 14
 − x − 4 y = −5       1+ 4 y = 5
      9x = 9         −1        −1
      9      9            4y = 4
                          4    4
     x=1
Example 1
          Solve by combining the equations
                      10x + 4 y = 14
                      
                   b. 
                       x + 4 y = 5)(−1)
                      (
10x + 4 y = 14
 − x − 4 y = −5       1+ 4 y = 5
      9x = 9         −1        −1
      9      9            4y = 4
                          4    4
     x=1
                          y =1
Example 1
          Solve by combining the equations
                      10x + 4 y = 14
                      
                   b. 
                       x + 4 y = 5)(−1)
                      (                   Check:
10x + 4 y = 14
 − x − 4 y = −5       1+ 4 y = 5
      9x = 9         −1        −1
      9      9            4y = 4
                          4    4
     x=1
                          y =1
Example 1
          Solve by combining the equations
                      10x + 4 y = 14
                      
                   b. 
                       x + 4 y = 5)(−1)
                      (                       Check:
10x + 4 y = 14
 − x − 4 y = −5       1+ 4 y = 5           10(1) + 4(1) = 14
      9x = 9         −1        −1
      9      9            4y = 4
                          4    4
     x=1
                          y =1
Example 1
          Solve by combining the equations
                      10x + 4 y = 14
                      
                   b. 
                       x + 4 y = 5)(−1)
                      (                       Check:
10x + 4 y = 14
 − x − 4 y = −5       1+ 4 y = 5           10(1) + 4(1) = 14
      9x = 9         −1        −1            10 + 4 = 14
      9      9            4y = 4
                          4    4
     x=1
                          y =1
Example 1
          Solve by combining the equations
                      10x + 4 y = 14
                      
                   b. 
                       x + 4 y = 5)(−1)
                      (                       Check:
10x + 4 y = 14
 − x − 4 y = −5       1+ 4 y = 5           10(1) + 4(1) = 14
      9x = 9         −1        −1            10 + 4 = 14
      9      9            4y = 4
                          4    4             1 + 4(1) = 5
     x=1
                          y =1
Example 1
          Solve by combining the equations
                      10x + 4 y = 14
                      
                   b. 
                       x + 4 y = 5)(−1)
                      (                       Check:
10x + 4 y = 14
 − x − 4 y = −5       1+ 4 y = 5           10(1) + 4(1) = 14
      9x = 9         −1        −1            10 + 4 = 14
      9      9            4y = 4
                          4    4             1 + 4(1) = 5
     x=1                                      1+ 4 = 5
                          y =1
Example 1
          Solve by combining the equations
                      10x + 4 y = 14
                      
                   b. 
                       x + 4 y = 5)(−1)
                      (                       Check:
10x + 4 y = 14
 − x − 4 y = −5       1+ 4 y = 5           10(1) + 4(1) = 14
      9x = 9         −1        −1            10 + 4 = 14
      9      9            4y = 4
                          4    4             1 + 4(1) = 5
     x=1                                      1+ 4 = 5
                          y =1
                                                (1,1)
Example 2
Solve by combining the equations
          7x + 2 y = 5
          
          
           2x + 3 y = 16
          
Example 2
Solve by combining the equations
          7x + 2 y = 5)(3)
          (
          
           2x + 3 y = 16
          
Example 2
Solve by combining the equations
          7x + 2 y = 5)(3)
          (
          
           2x + 3 y = 16)(−2)
          (
Example 2
       Solve by combining the equations
                   7x + 2 y = 5)(3)
                   (
                   
                    2x + 3 y = 16)(−2)
                   (
21x + 6 y = 15
Example 2
       Solve by combining the equations
                  7x + 2 y = 5)(3)
                  (
                  
                   2x + 3 y = 16)(−2)
                  (
21x + 6 y = 15
−4x − 6 y = −32
Example 2
       Solve by combining the equations
                  7x + 2 y = 5)(3)
                  (
                  
                   2x + 3 y = 16)(−2)
                  (
21x + 6 y = 15
−4x − 6 y = −32
Example 2
       Solve by combining the equations
                  7x + 2 y = 5)(3)
                  (
                  
                   2x + 3 y = 16)(−2)
                  (
21x + 6 y = 15
−4x − 6 y = −32
    17x = −17
Example 2
       Solve by combining the equations
                  7x + 2 y = 5)(3)
                  (
                  
                   2x + 3 y = 16)(−2)
                  (
21x + 6 y = 15
−4x − 6 y = −32
    17x = −17
     17    17
Example 2
       Solve by combining the equations
                  7x + 2 y = 5)(3)
                  (
                  
                   2x + 3 y = 16)(−2)
                  (
21x + 6 y = 15
−4x − 6 y = −32
    17x = −17
     17    17
      x = −1
Example 2
       Solve by combining the equations
                   7x + 2 y = 5)(3)
                   (
                   
                    2x + 3 y = 16)(−2)
                   (
21x + 6 y = 15    2(−1) + 3 y = 16
−4x − 6 y = −32
    17x = −17
     17    17
      x = −1
Example 2
       Solve by combining the equations
                   7x + 2 y = 5)(3)
                   (
                   
                    2x + 3 y = 16)(−2)
                   (
21x + 6 y = 15    2(−1) + 3 y = 16
−4x − 6 y = −32     −2 + 3 y = 16
    17x = −17
     17    17
      x = −1
Example 2
       Solve by combining the equations
                   7x + 2 y = 5)(3)
                   (
                   
                    2x + 3 y = 16)(−2)
                   (
21x + 6 y = 15    2(−1) + 3 y = 16
−4x − 6 y = −32     −2 + 3 y = 16
    17x = −17      +2         +2
     17    17
      x = −1
Example 2
       Solve by combining the equations
                   7x + 2 y = 5)(3)
                   (
                   
                    2x + 3 y = 16)(−2)
                   (
21x + 6 y = 15    2(−1) + 3 y = 16
−4x − 6 y = −32     −2 + 3 y = 16
    17x = −17      +2         +2
     17    17           3 y = 18
      x = −1
Example 2
       Solve by combining the equations
                   7x + 2 y = 5)(3)
                   (
                   
                    2x + 3 y = 16)(−2)
                   (
21x + 6 y = 15    2(−1) + 3 y = 16
−4x − 6 y = −32     −2 + 3 y = 16
    17x = −17      +2         +2
     17    17           3 y = 18
      x = −1            3     3
Example 2
       Solve by combining the equations
                   7x + 2 y = 5)(3)
                   (
                   
                    2x + 3 y = 16)(−2)
                   (
21x + 6 y = 15    2(−1) + 3 y = 16
−4x − 6 y = −32     −2 + 3 y = 16
    17x = −17      +2         +2
     17    17           3 y = 18
      x = −1            3      3
                         y=6
Example 2
       Solve by combining the equations
                   7x + 2 y = 5)(3)
                   (
                   
                    2x + 3 y = 16)(−2)
                   (
                                          Check:
21x + 6 y = 15    2(−1) + 3 y = 16
−4x − 6 y = −32     −2 + 3 y = 16
    17x = −17      +2         +2
     17    17           3 y = 18
      x = −1            3      3
                         y=6
Example 2
       Solve by combining the equations
                   7x + 2 y = 5)(3)
                   (
                   
                    2x + 3 y = 16)(−2)
                   (
                                           Check:
21x + 6 y = 15    2(−1) + 3 y = 16
−4x − 6 y = −32                         7(−1) + 2(6) = 5
                    −2 + 3 y = 16
    17x = −17      +2         +2
     17    17           3 y = 18
      x = −1            3      3
                         y=6
Example 2
       Solve by combining the equations
                   7x + 2 y = 5)(3)
                   (
                   
                    2x + 3 y = 16)(−2)
                   (
                                           Check:
21x + 6 y = 15    2(−1) + 3 y = 16
−4x − 6 y = −32                         7(−1) + 2(6) = 5
                    −2 + 3 y = 16
                                          −7 + 12 = 5
    17x = −17      +2          +2
     17    17           3 y = 18
      x = −1            3      3
                         y=6
Example 2
       Solve by combining the equations
                   7x + 2 y = 5)(3)
                   (
                   
                    2x + 3 y = 16)(−2)
                   (
                                           Check:
21x + 6 y = 15    2(−1) + 3 y = 16
−4x − 6 y = −32                         7(−1) + 2(6) = 5
                    −2 + 3 y = 16
                                          −7 + 12 = 5
    17x = −17      +2          +2
     17    17           3 y = 18         2(−1) + 3(6) = 16
      x = −1            3      3
                         y=6
Example 2
       Solve by combining the equations
                   7x + 2 y = 5)(3)
                   (
                   
                    2x + 3 y = 16)(−2)
                   (
                                           Check:
21x + 6 y = 15    2(−1) + 3 y = 16
−4x − 6 y = −32                         7(−1) + 2(6) = 5
                    −2 + 3 y = 16
                                          −7 + 12 = 5
    17x = −17      +2          +2
     17    17           3 y = 18         2(−1) + 3(6) = 16
      x = −1            3      3          −2 + 18 = 16
                         y=6
Example 2
       Solve by combining the equations
                   7x + 2 y = 5)(3)
                   (
                   
                    2x + 3 y = 16)(−2)
                   (
                                           Check:
21x + 6 y = 15    2(−1) + 3 y = 16
−4x − 6 y = −32                         7(−1) + 2(6) = 5
                    −2 + 3 y = 16
                                          −7 + 12 = 5
    17x = −17      +2          +2
     17    17           3 y = 18         2(−1) + 3(6) = 16
      x = −1            3      3          −2 + 18 = 16
                         y=6
                                             (−1, 6)
Example 3
Solve by combining the equations
          5x + 2 y = 7
          
          
          4x + 2 y = −3
          
Example 3
Solve by combining the equations
          5x + 2 y = 7
          
          
          4x + 2 y = −3)(−1)
          (
Example 3
     Solve by combining the equations
               5x + 2 y = 7
               
               
               4x + 2 y = −3)(−1)
               (
5x + 2 y = 7
Example 3
      Solve by combining the equations
                5x + 2 y = 7
                
                
                4x + 2 y = −3)(−1)
                (
 5x + 2 y = 7
−4x − 2 y = 3
Example 3
      Solve by combining the equations
                5x + 2 y = 7
                
                
                4x + 2 y = −3)(−1)
                (
 5x + 2 y = 7
−4x − 2 y = 3
Example 3
      Solve by combining the equations
                5x + 2 y = 7
                
                
                4x + 2 y = −3)(−1)
                (
 5x + 2 y = 7
−4x − 2 y = 3
       x = 10
Example 3
      Solve by combining the equations
                5x + 2 y = 7
                
                
                4x + 2 y = −3)(−1)
                (
 5x + 2 y = 7   5(10) + 2 y = 7
−4x − 2 y = 3
       x = 10
Example 3
      Solve by combining the equations
                5x + 2 y = 7
                
                
                4x + 2 y = −3)(−1)
                (
 5x + 2 y = 7   5(10) + 2 y = 7
−4x − 2 y = 3     50 + 2 y = 7
       x = 10
Example 3
      Solve by combining the equations
                5x + 2 y = 7
                
                
                4x + 2 y = −3)(−1)
                (
 5x + 2 y = 7   5(10) + 2 y = 7
−4x − 2 y = 3     50 + 2 y = 7
                −50        −50
       x = 10
Example 3
      Solve by combining the equations
                5x + 2 y = 7
                
                
                4x + 2 y = −3)(−1)
                (
 5x + 2 y = 7   5(10) + 2 y = 7
−4x − 2 y = 3     50 + 2 y = 7
                −50        −50
       x = 10
                      2 y = −43
Example 3
      Solve by combining the equations
                5x + 2 y = 7
                
                
                4x + 2 y = −3)(−1)
                (
 5x + 2 y = 7   5(10) + 2 y = 7
−4x − 2 y = 3     50 + 2 y = 7
                −50        −50
       x = 10
                      2 y = −43
                       2     2
Example 3
      Solve by combining the equations
                5x + 2 y = 7
                
                
                4x + 2 y = −3)(−1)
                (
 5x + 2 y = 7   5(10) + 2 y = 7
−4x − 2 y = 3     50 + 2 y = 7
                −50        −50
       x = 10
                      2 y = −43
                       2     2
                       −43
                    y=
                        2
Example 3
      Solve by combining the equations
                5x + 2 y = 7
                
                
                4x + 2 y = −3)(−1)
                (
                                      Check:
 5x + 2 y = 7   5(10) + 2 y = 7
−4x − 2 y = 3     50 + 2 y = 7
                −50        −50
       x = 10
                      2 y = −43
                       2     2
                       −43
                    y=
                        2
Example 3
      Solve by combining the equations
                5x + 2 y = 7
                
                
                4x + 2 y = −3)(−1)
                (
                                          Check:
 5x + 2 y = 7   5(10) + 2 y = 7       5(10) + 2(− ) = 7
                                                 43

−4x − 2 y = 3     50 + 2 y = 7                    2

                −50        −50
       x = 10
                      2 y = −43
                       2     2
                       −43
                    y=
                        2
Example 3
      Solve by combining the equations
                5x + 2 y = 7
                
                
                4x + 2 y = −3)(−1)
                (
                                          Check:
 5x + 2 y = 7   5(10) + 2 y = 7       5(10) + 2(− ) = 7
                                                 43

−4x − 2 y = 3     50 + 2 y = 7                    2

                −50                      50 − 43 = 7
                           −50
       x = 10
                      2 y = −43
                       2     2
                       −43
                    y=
                        2
Example 3
      Solve by combining the equations
                5x + 2 y = 7
                
                
                4x + 2 y = −3)(−1)
                (
                                          Check:
 5x + 2 y = 7   5(10) + 2 y = 7       5(10) + 2(− ) = 7
                                                 43

−4x − 2 y = 3     50 + 2 y = 7                    2

                −50                      50 − 43 = 7
                           −50
       x = 10
                      2 y = −43       4(10) + 2(− ) = −3
                                                43
                                                 2

                       2     2
                       −43
                    y=
                        2
Example 3
      Solve by combining the equations
                5x + 2 y = 7
                
                
                4x + 2 y = −3)(−1)
                (
                                          Check:
 5x + 2 y = 7   5(10) + 2 y = 7       5(10) + 2(− ) = 7
                                                 43

−4x − 2 y = 3     50 + 2 y = 7                    2

                −50                      50 − 43 = 7
                           −50
       x = 10
                      2 y = −43       4(10) + 2(− ) = −3
                                                43
                                                 2

                       2     2           40 − 43 = −3
                       −43
                    y=
                        2
Example 3
      Solve by combining the equations
                5x + 2 y = 7
                
                
                4x + 2 y = −3)(−1)
                (
                                          Check:
 5x + 2 y = 7   5(10) + 2 y = 7       5(10) + 2(− ) = 7
                                                 43

−4x − 2 y = 3     50 + 2 y = 7                    2

                −50                      50 − 43 = 7
                           −50
       x = 10
                      2 y = −43       4(10) + 2(− ) = −3
                                                43
                                                 2

                       2     2           40 − 43 = −3
                       −43
                    y=
                        2
                                        (10, − ) 43
                                                  2
Homework
Homework

             p. 350 #1-27 odd




“A verbal contract isn’t worth the paper it’s
      written on.” - Samuel Goldwyn

Integrated Math 2 Section 8-4

  • 1.
    Section 8-4 Solve Systemsby Adding, Subtracting, and Multiplying (Linear Combinations)
  • 2.
    Essential Questions Howdo you solve systems of equations by adding and subtracting? How do you solve systems of equations by adding and multiplying? Where you’ll see this: Landscaping, construction, sports
  • 3.
  • 4.
    Why another method? Graphing: Problems with accuracy
  • 5.
    Why another method? Graphing: Problems with accuracy Substitution: Need an isolated variable
  • 6.
    Why another method? Graphing: Problems with accuracy Substitution: Need an isolated variable Combinations: Could speed up process
  • 7.
    Why another method? Graphing: Problems with accuracy Substitution: Need an isolated variable Combinations: Could speed up process Look at the system to determine best method
  • 8.
  • 9.
    Solve by Combinations 1.Choose a variable to eliminate (your choice).
  • 10.
    Solve by Combinations 1.Choose a variable to eliminate (your choice). 2. Make the coefficients of that variable opposite. You might need to multiply to do this. Then combine equations.
  • 11.
    Solve by Combinations 1.Choose a variable to eliminate (your choice). 2. Make the coefficients of that variable opposite. You might need to multiply to do this. Then combine equations. 3. Solve for the remaining variable.
  • 12.
    Solve by Combinations 1.Choose a variable to eliminate (your choice). 2. Make the coefficients of that variable opposite. You might need to multiply to do this. Then combine equations. 3. Solve for the remaining variable. 4. Plug back into an original equation to find the other variable.
  • 13.
    Solve by Combinations 1.Choose a variable to eliminate (your choice). 2. Make the coefficients of that variable opposite. You might need to multiply to do this. Then combine equations. 3. Solve for the remaining variable. 4. Plug back into an original equation to find the other variable. 5. Check and rewrite the answer.
  • 14.
    Example 1 Solve bycombining the equations −2x + 3 y = 2  a.   2x + 7 y = 18 
  • 15.
    Example 1 Solve by combining the equations −2x + 3 y = 2  a.   2x + 7 y = 18  −2x + 3 y = 2
  • 16.
    Example 1 Solve by combining the equations −2x + 3 y = 2  a.   2x + 7 y = 18  −2x + 3 y = 2 2x + 7 y = 18
  • 17.
    Example 1 Solve by combining the equations −2x + 3 y = 2  a.   2x + 7 y = 18  −2x + 3 y = 2 2x + 7 y = 18
  • 18.
    Example 1 Solve by combining the equations −2x + 3 y = 2  a.   2x + 7 y = 18  −2x + 3 y = 2 2x + 7 y = 18 10 y = 20
  • 19.
    Example 1 Solve by combining the equations −2x + 3 y = 2  a.   2x + 7 y = 18  −2x + 3 y = 2 2x + 7 y = 18 10 y = 20 10 10
  • 20.
    Example 1 Solve by combining the equations −2x + 3 y = 2  a.   2x + 7 y = 18  −2x + 3 y = 2 2x + 7 y = 18 10 y = 20 10 10 y=2
  • 21.
    Example 1 Solve by combining the equations −2x + 3 y = 2  a.   2x + 7 y = 18  −2x + 3 y = 2 −2x + 3(2) = 2 2x + 7 y = 18 10 y = 20 10 10 y=2
  • 22.
    Example 1 Solve by combining the equations −2x + 3 y = 2  a.   2x + 7 y = 18  −2x + 3 y = 2 −2x + 3(2) = 2 2x + 7 y = 18 −2x + 6 = 2 10 y = 20 10 10 y=2
  • 23.
    Example 1 Solve by combining the equations −2x + 3 y = 2  a.   2x + 7 y = 18  −2x + 3 y = 2 −2x + 3(2) = 2 2x + 7 y = 18 −2x + 6 = 2 10 y = 20 −6 −6 10 10 y=2
  • 24.
    Example 1 Solve by combining the equations −2x + 3 y = 2  a.   2x + 7 y = 18  −2x + 3 y = 2 −2x + 3(2) = 2 2x + 7 y = 18 −2x + 6 = 2 10 y = 20 −6 −6 10 10 −2x = −4 y=2
  • 25.
    Example 1 Solve by combining the equations −2x + 3 y = 2  a.   2x + 7 y = 18  −2x + 3 y = 2 −2x + 3(2) = 2 2x + 7 y = 18 −2x + 6 = 2 10 y = 20 −6 −6 10 10 −2x = −4 y=2 −2 −2
  • 26.
    Example 1 Solve by combining the equations −2x + 3 y = 2  a.   2x + 7 y = 18  −2x + 3 y = 2 −2x + 3(2) = 2 2x + 7 y = 18 −2x + 6 = 2 10 y = 20 −6 −6 10 10 −2x = −4 y=2 −2 −2 x=2
  • 27.
    Example 1 Solve by combining the equations −2x + 3 y = 2  a.   2x + 7 y = 18  Check: −2x + 3 y = 2 −2x + 3(2) = 2 2x + 7 y = 18 −2x + 6 = 2 10 y = 20 −6 −6 10 10 −2x = −4 y=2 −2 −2 x=2
  • 28.
    Example 1 Solve by combining the equations −2x + 3 y = 2  a.   2x + 7 y = 18  Check: −2x + 3 y = 2 −2(2) + 3(2) = 2 −2x + 3(2) = 2 2x + 7 y = 18 −2x + 6 = 2 10 y = 20 −6 −6 10 10 −2x = −4 y=2 −2 −2 x=2
  • 29.
    Example 1 Solve by combining the equations −2x + 3 y = 2  a.   2x + 7 y = 18  Check: −2x + 3 y = 2 −2(2) + 3(2) = 2 −2x + 3(2) = 2 2x + 7 y = 18 −4 + 6 = 2 −2x + 6 = 2 10 y = 20 −6 −6 10 10 −2x = −4 y=2 −2 −2 x=2
  • 30.
    Example 1 Solve by combining the equations −2x + 3 y = 2  a.   2x + 7 y = 18  Check: −2x + 3 y = 2 −2(2) + 3(2) = 2 −2x + 3(2) = 2 2x + 7 y = 18 −4 + 6 = 2 −2x + 6 = 2 10 y = 20 −6 −6 2(2) + 7(2) = 18 10 10 −2x = −4 y=2 −2 −2 x=2
  • 31.
    Example 1 Solve by combining the equations −2x + 3 y = 2  a.   2x + 7 y = 18  Check: −2x + 3 y = 2 −2(2) + 3(2) = 2 −2x + 3(2) = 2 2x + 7 y = 18 −4 + 6 = 2 −2x + 6 = 2 10 y = 20 −6 −6 2(2) + 7(2) = 18 10 10 −2x = −4 4 + 14 = 18 y=2 −2 −2 x=2
  • 32.
    Example 1 Solve by combining the equations −2x + 3 y = 2  a.   2x + 7 y = 18  Check: −2x + 3 y = 2 −2(2) + 3(2) = 2 −2x + 3(2) = 2 2x + 7 y = 18 −4 + 6 = 2 −2x + 6 = 2 10 y = 20 −6 −6 2(2) + 7(2) = 18 10 10 −2x = −4 4 + 14 = 18 y=2 −2 −2 x=2 (2, 2)
  • 33.
    Example 1 Solve bycombining the equations 10x + 4 y = 14  b.  x + 4 y = 5 
  • 34.
    Example 1 Solve bycombining the equations 10x + 4 y = 14  b.   x + 4 y = 5)(−1) (
  • 35.
    Example 1 Solve by combining the equations 10x + 4 y = 14  b.   x + 4 y = 5)(−1) ( 10x + 4 y = 14
  • 36.
    Example 1 Solve by combining the equations 10x + 4 y = 14  b.   x + 4 y = 5)(−1) ( 10x + 4 y = 14 − x − 4 y = −5
  • 37.
    Example 1 Solve by combining the equations 10x + 4 y = 14  b.   x + 4 y = 5)(−1) ( 10x + 4 y = 14 − x − 4 y = −5
  • 38.
    Example 1 Solve by combining the equations 10x + 4 y = 14  b.   x + 4 y = 5)(−1) ( 10x + 4 y = 14 − x − 4 y = −5 9x = 9
  • 39.
    Example 1 Solve by combining the equations 10x + 4 y = 14  b.   x + 4 y = 5)(−1) ( 10x + 4 y = 14 − x − 4 y = −5 9x = 9 9 9
  • 40.
    Example 1 Solve by combining the equations 10x + 4 y = 14  b.   x + 4 y = 5)(−1) ( 10x + 4 y = 14 − x − 4 y = −5 9x = 9 9 9 x=1
  • 41.
    Example 1 Solve by combining the equations 10x + 4 y = 14  b.   x + 4 y = 5)(−1) ( 10x + 4 y = 14 − x − 4 y = −5 1+ 4 y = 5 9x = 9 9 9 x=1
  • 42.
    Example 1 Solve by combining the equations 10x + 4 y = 14  b.   x + 4 y = 5)(−1) ( 10x + 4 y = 14 − x − 4 y = −5 1+ 4 y = 5 9x = 9 −1 −1 9 9 x=1
  • 43.
    Example 1 Solve by combining the equations 10x + 4 y = 14  b.   x + 4 y = 5)(−1) ( 10x + 4 y = 14 − x − 4 y = −5 1+ 4 y = 5 9x = 9 −1 −1 9 9 4y = 4 x=1
  • 44.
    Example 1 Solve by combining the equations 10x + 4 y = 14  b.   x + 4 y = 5)(−1) ( 10x + 4 y = 14 − x − 4 y = −5 1+ 4 y = 5 9x = 9 −1 −1 9 9 4y = 4 4 4 x=1
  • 45.
    Example 1 Solve by combining the equations 10x + 4 y = 14  b.   x + 4 y = 5)(−1) ( 10x + 4 y = 14 − x − 4 y = −5 1+ 4 y = 5 9x = 9 −1 −1 9 9 4y = 4 4 4 x=1 y =1
  • 46.
    Example 1 Solve by combining the equations 10x + 4 y = 14  b.   x + 4 y = 5)(−1) ( Check: 10x + 4 y = 14 − x − 4 y = −5 1+ 4 y = 5 9x = 9 −1 −1 9 9 4y = 4 4 4 x=1 y =1
  • 47.
    Example 1 Solve by combining the equations 10x + 4 y = 14  b.   x + 4 y = 5)(−1) ( Check: 10x + 4 y = 14 − x − 4 y = −5 1+ 4 y = 5 10(1) + 4(1) = 14 9x = 9 −1 −1 9 9 4y = 4 4 4 x=1 y =1
  • 48.
    Example 1 Solve by combining the equations 10x + 4 y = 14  b.   x + 4 y = 5)(−1) ( Check: 10x + 4 y = 14 − x − 4 y = −5 1+ 4 y = 5 10(1) + 4(1) = 14 9x = 9 −1 −1 10 + 4 = 14 9 9 4y = 4 4 4 x=1 y =1
  • 49.
    Example 1 Solve by combining the equations 10x + 4 y = 14  b.   x + 4 y = 5)(−1) ( Check: 10x + 4 y = 14 − x − 4 y = −5 1+ 4 y = 5 10(1) + 4(1) = 14 9x = 9 −1 −1 10 + 4 = 14 9 9 4y = 4 4 4 1 + 4(1) = 5 x=1 y =1
  • 50.
    Example 1 Solve by combining the equations 10x + 4 y = 14  b.   x + 4 y = 5)(−1) ( Check: 10x + 4 y = 14 − x − 4 y = −5 1+ 4 y = 5 10(1) + 4(1) = 14 9x = 9 −1 −1 10 + 4 = 14 9 9 4y = 4 4 4 1 + 4(1) = 5 x=1 1+ 4 = 5 y =1
  • 51.
    Example 1 Solve by combining the equations 10x + 4 y = 14  b.   x + 4 y = 5)(−1) ( Check: 10x + 4 y = 14 − x − 4 y = −5 1+ 4 y = 5 10(1) + 4(1) = 14 9x = 9 −1 −1 10 + 4 = 14 9 9 4y = 4 4 4 1 + 4(1) = 5 x=1 1+ 4 = 5 y =1 (1,1)
  • 52.
    Example 2 Solve bycombining the equations 7x + 2 y = 5    2x + 3 y = 16 
  • 53.
    Example 2 Solve bycombining the equations 7x + 2 y = 5)(3) (   2x + 3 y = 16 
  • 54.
    Example 2 Solve bycombining the equations 7x + 2 y = 5)(3) (   2x + 3 y = 16)(−2) (
  • 55.
    Example 2 Solve by combining the equations 7x + 2 y = 5)(3) (   2x + 3 y = 16)(−2) ( 21x + 6 y = 15
  • 56.
    Example 2 Solve by combining the equations 7x + 2 y = 5)(3) (   2x + 3 y = 16)(−2) ( 21x + 6 y = 15 −4x − 6 y = −32
  • 57.
    Example 2 Solve by combining the equations 7x + 2 y = 5)(3) (   2x + 3 y = 16)(−2) ( 21x + 6 y = 15 −4x − 6 y = −32
  • 58.
    Example 2 Solve by combining the equations 7x + 2 y = 5)(3) (   2x + 3 y = 16)(−2) ( 21x + 6 y = 15 −4x − 6 y = −32 17x = −17
  • 59.
    Example 2 Solve by combining the equations 7x + 2 y = 5)(3) (   2x + 3 y = 16)(−2) ( 21x + 6 y = 15 −4x − 6 y = −32 17x = −17 17 17
  • 60.
    Example 2 Solve by combining the equations 7x + 2 y = 5)(3) (   2x + 3 y = 16)(−2) ( 21x + 6 y = 15 −4x − 6 y = −32 17x = −17 17 17 x = −1
  • 61.
    Example 2 Solve by combining the equations 7x + 2 y = 5)(3) (   2x + 3 y = 16)(−2) ( 21x + 6 y = 15 2(−1) + 3 y = 16 −4x − 6 y = −32 17x = −17 17 17 x = −1
  • 62.
    Example 2 Solve by combining the equations 7x + 2 y = 5)(3) (   2x + 3 y = 16)(−2) ( 21x + 6 y = 15 2(−1) + 3 y = 16 −4x − 6 y = −32 −2 + 3 y = 16 17x = −17 17 17 x = −1
  • 63.
    Example 2 Solve by combining the equations 7x + 2 y = 5)(3) (   2x + 3 y = 16)(−2) ( 21x + 6 y = 15 2(−1) + 3 y = 16 −4x − 6 y = −32 −2 + 3 y = 16 17x = −17 +2 +2 17 17 x = −1
  • 64.
    Example 2 Solve by combining the equations 7x + 2 y = 5)(3) (   2x + 3 y = 16)(−2) ( 21x + 6 y = 15 2(−1) + 3 y = 16 −4x − 6 y = −32 −2 + 3 y = 16 17x = −17 +2 +2 17 17 3 y = 18 x = −1
  • 65.
    Example 2 Solve by combining the equations 7x + 2 y = 5)(3) (   2x + 3 y = 16)(−2) ( 21x + 6 y = 15 2(−1) + 3 y = 16 −4x − 6 y = −32 −2 + 3 y = 16 17x = −17 +2 +2 17 17 3 y = 18 x = −1 3 3
  • 66.
    Example 2 Solve by combining the equations 7x + 2 y = 5)(3) (   2x + 3 y = 16)(−2) ( 21x + 6 y = 15 2(−1) + 3 y = 16 −4x − 6 y = −32 −2 + 3 y = 16 17x = −17 +2 +2 17 17 3 y = 18 x = −1 3 3 y=6
  • 67.
    Example 2 Solve by combining the equations 7x + 2 y = 5)(3) (   2x + 3 y = 16)(−2) ( Check: 21x + 6 y = 15 2(−1) + 3 y = 16 −4x − 6 y = −32 −2 + 3 y = 16 17x = −17 +2 +2 17 17 3 y = 18 x = −1 3 3 y=6
  • 68.
    Example 2 Solve by combining the equations 7x + 2 y = 5)(3) (   2x + 3 y = 16)(−2) ( Check: 21x + 6 y = 15 2(−1) + 3 y = 16 −4x − 6 y = −32 7(−1) + 2(6) = 5 −2 + 3 y = 16 17x = −17 +2 +2 17 17 3 y = 18 x = −1 3 3 y=6
  • 69.
    Example 2 Solve by combining the equations 7x + 2 y = 5)(3) (   2x + 3 y = 16)(−2) ( Check: 21x + 6 y = 15 2(−1) + 3 y = 16 −4x − 6 y = −32 7(−1) + 2(6) = 5 −2 + 3 y = 16 −7 + 12 = 5 17x = −17 +2 +2 17 17 3 y = 18 x = −1 3 3 y=6
  • 70.
    Example 2 Solve by combining the equations 7x + 2 y = 5)(3) (   2x + 3 y = 16)(−2) ( Check: 21x + 6 y = 15 2(−1) + 3 y = 16 −4x − 6 y = −32 7(−1) + 2(6) = 5 −2 + 3 y = 16 −7 + 12 = 5 17x = −17 +2 +2 17 17 3 y = 18 2(−1) + 3(6) = 16 x = −1 3 3 y=6
  • 71.
    Example 2 Solve by combining the equations 7x + 2 y = 5)(3) (   2x + 3 y = 16)(−2) ( Check: 21x + 6 y = 15 2(−1) + 3 y = 16 −4x − 6 y = −32 7(−1) + 2(6) = 5 −2 + 3 y = 16 −7 + 12 = 5 17x = −17 +2 +2 17 17 3 y = 18 2(−1) + 3(6) = 16 x = −1 3 3 −2 + 18 = 16 y=6
  • 72.
    Example 2 Solve by combining the equations 7x + 2 y = 5)(3) (   2x + 3 y = 16)(−2) ( Check: 21x + 6 y = 15 2(−1) + 3 y = 16 −4x − 6 y = −32 7(−1) + 2(6) = 5 −2 + 3 y = 16 −7 + 12 = 5 17x = −17 +2 +2 17 17 3 y = 18 2(−1) + 3(6) = 16 x = −1 3 3 −2 + 18 = 16 y=6 (−1, 6)
  • 73.
    Example 3 Solve bycombining the equations 5x + 2 y = 7   4x + 2 y = −3 
  • 74.
    Example 3 Solve bycombining the equations 5x + 2 y = 7   4x + 2 y = −3)(−1) (
  • 75.
    Example 3 Solve by combining the equations 5x + 2 y = 7   4x + 2 y = −3)(−1) ( 5x + 2 y = 7
  • 76.
    Example 3 Solve by combining the equations 5x + 2 y = 7   4x + 2 y = −3)(−1) ( 5x + 2 y = 7 −4x − 2 y = 3
  • 77.
    Example 3 Solve by combining the equations 5x + 2 y = 7   4x + 2 y = −3)(−1) ( 5x + 2 y = 7 −4x − 2 y = 3
  • 78.
    Example 3 Solve by combining the equations 5x + 2 y = 7   4x + 2 y = −3)(−1) ( 5x + 2 y = 7 −4x − 2 y = 3 x = 10
  • 79.
    Example 3 Solve by combining the equations 5x + 2 y = 7   4x + 2 y = −3)(−1) ( 5x + 2 y = 7 5(10) + 2 y = 7 −4x − 2 y = 3 x = 10
  • 80.
    Example 3 Solve by combining the equations 5x + 2 y = 7   4x + 2 y = −3)(−1) ( 5x + 2 y = 7 5(10) + 2 y = 7 −4x − 2 y = 3 50 + 2 y = 7 x = 10
  • 81.
    Example 3 Solve by combining the equations 5x + 2 y = 7   4x + 2 y = −3)(−1) ( 5x + 2 y = 7 5(10) + 2 y = 7 −4x − 2 y = 3 50 + 2 y = 7 −50 −50 x = 10
  • 82.
    Example 3 Solve by combining the equations 5x + 2 y = 7   4x + 2 y = −3)(−1) ( 5x + 2 y = 7 5(10) + 2 y = 7 −4x − 2 y = 3 50 + 2 y = 7 −50 −50 x = 10 2 y = −43
  • 83.
    Example 3 Solve by combining the equations 5x + 2 y = 7   4x + 2 y = −3)(−1) ( 5x + 2 y = 7 5(10) + 2 y = 7 −4x − 2 y = 3 50 + 2 y = 7 −50 −50 x = 10 2 y = −43 2 2
  • 84.
    Example 3 Solve by combining the equations 5x + 2 y = 7   4x + 2 y = −3)(−1) ( 5x + 2 y = 7 5(10) + 2 y = 7 −4x − 2 y = 3 50 + 2 y = 7 −50 −50 x = 10 2 y = −43 2 2 −43 y= 2
  • 85.
    Example 3 Solve by combining the equations 5x + 2 y = 7   4x + 2 y = −3)(−1) ( Check: 5x + 2 y = 7 5(10) + 2 y = 7 −4x − 2 y = 3 50 + 2 y = 7 −50 −50 x = 10 2 y = −43 2 2 −43 y= 2
  • 86.
    Example 3 Solve by combining the equations 5x + 2 y = 7   4x + 2 y = −3)(−1) ( Check: 5x + 2 y = 7 5(10) + 2 y = 7 5(10) + 2(− ) = 7 43 −4x − 2 y = 3 50 + 2 y = 7 2 −50 −50 x = 10 2 y = −43 2 2 −43 y= 2
  • 87.
    Example 3 Solve by combining the equations 5x + 2 y = 7   4x + 2 y = −3)(−1) ( Check: 5x + 2 y = 7 5(10) + 2 y = 7 5(10) + 2(− ) = 7 43 −4x − 2 y = 3 50 + 2 y = 7 2 −50 50 − 43 = 7 −50 x = 10 2 y = −43 2 2 −43 y= 2
  • 88.
    Example 3 Solve by combining the equations 5x + 2 y = 7   4x + 2 y = −3)(−1) ( Check: 5x + 2 y = 7 5(10) + 2 y = 7 5(10) + 2(− ) = 7 43 −4x − 2 y = 3 50 + 2 y = 7 2 −50 50 − 43 = 7 −50 x = 10 2 y = −43 4(10) + 2(− ) = −3 43 2 2 2 −43 y= 2
  • 89.
    Example 3 Solve by combining the equations 5x + 2 y = 7   4x + 2 y = −3)(−1) ( Check: 5x + 2 y = 7 5(10) + 2 y = 7 5(10) + 2(− ) = 7 43 −4x − 2 y = 3 50 + 2 y = 7 2 −50 50 − 43 = 7 −50 x = 10 2 y = −43 4(10) + 2(− ) = −3 43 2 2 2 40 − 43 = −3 −43 y= 2
  • 90.
    Example 3 Solve by combining the equations 5x + 2 y = 7   4x + 2 y = −3)(−1) ( Check: 5x + 2 y = 7 5(10) + 2 y = 7 5(10) + 2(− ) = 7 43 −4x − 2 y = 3 50 + 2 y = 7 2 −50 50 − 43 = 7 −50 x = 10 2 y = −43 4(10) + 2(− ) = −3 43 2 2 2 40 − 43 = −3 −43 y= 2 (10, − ) 43 2
  • 91.
  • 92.
    Homework p. 350 #1-27 odd “A verbal contract isn’t worth the paper it’s written on.” - Samuel Goldwyn