Factoring Quadratic
   Expressions
WAYS TO SOLVE A QUADRATIC
   EQUATION ax² + bx + c = 0

• There are many ways to solve a quadratic.
• The main ones are:
  – Graphing
  – Factoring
  – Bottom’s Up
  – Grouping
  – Quadratic formula
  – Completing the square
By Graphing
         y = (x + 2)(x – 4)




By looking at the roots, we can get the solutions.
Here, the solutions are -2 and 4.
Golden Rules of Factoring
Example: Factor out the greatest
        common factor
• 4x2 + 20x -12
Practice: Factor each expression

a)   9x2 + 3x – 18   Solutions:
                     a.) 3(3x2 + x – 6)

b)   7p2 + 21
                     b)   7(p2 + 3)

c)   4w2 + 2w
                     c)   2w(2w + 1)
Factor Diamonds

   x² + 8x + 7 =0
        7
    7       1
        8


 = (x + 1) (x + 7) = 0

 So your answers are -1 and -7
Practice: Solve by a factor diamond
• X2 + 15x + 36




                          (x+3)(x+12)
Bottom’s up (Borrowing Method)

         2x² + 13x + 6 =0
         x² + 13x + 12 =0           12
                               12        1
      = (x + 12) (x + 1) =0         13
              2        2
        = (x + 6) (x + 1) =0   Multiply by 2 to
                       2       get rid of the
                               fraction

       = (x + 6) (2x + 1) =0
           So your answers are -6 and -1/2
Practice: Solve using
  Bottom’s Up/Barrowing Method
• 2x2 – 19x + 24




                        (x-8)(2x-3)
Factor by Grouping

            2x² – 7x – 15 =0
   -30    2x² – 10x + 3x – 15 =0
-10 3
   -7                                 Note: you are
                                      on the right
            2x(x – 5) + 3(x – 5) =0   track because
                                      you have (x-5)
                                      in both
           (2x + 3)(x – 5)=0          parenthesis



    So your answers are -3/2 and 5
Practice: Factor by Grouping
3x2 + 7x - 20




                       (x+4)(3x-5)
SHORTCUTS
• a2 + 2ab + b2               (a+b)2
   Example: 25x2 + 90x + 81     (5x + 9)2


• a2 - 2ab + b2               (a - b)2
   Example: 9x2 – 42x + 49      (3x – 7)2




• a2 - b2                      (a+b)(a - b)
   Example: x2 – 64             (x + 8)(x – 8)
Practice Problems: Solve using any
              method

                     Solutions:
•   3x2 – 16x – 12
                     a)(x-6)(3x+2)
•   4x2 + 5x – 6
•   4x2 – 49         c) (x+2)(4x-3)

•   2x2 + 11X + 12   d)(2x+7)(2x-7)
                     e)(x+4)(2x+3)

Factoring quadratic expressions

  • 1.
  • 2.
    WAYS TO SOLVEA QUADRATIC EQUATION ax² + bx + c = 0 • There are many ways to solve a quadratic. • The main ones are: – Graphing – Factoring – Bottom’s Up – Grouping – Quadratic formula – Completing the square
  • 3.
    By Graphing y = (x + 2)(x – 4) By looking at the roots, we can get the solutions. Here, the solutions are -2 and 4.
  • 4.
    Golden Rules ofFactoring
  • 5.
    Example: Factor outthe greatest common factor • 4x2 + 20x -12
  • 6.
    Practice: Factor eachexpression a) 9x2 + 3x – 18 Solutions: a.) 3(3x2 + x – 6) b) 7p2 + 21 b) 7(p2 + 3) c) 4w2 + 2w c) 2w(2w + 1)
  • 7.
    Factor Diamonds x² + 8x + 7 =0 7 7 1 8 = (x + 1) (x + 7) = 0 So your answers are -1 and -7
  • 8.
    Practice: Solve bya factor diamond • X2 + 15x + 36 (x+3)(x+12)
  • 9.
    Bottom’s up (BorrowingMethod) 2x² + 13x + 6 =0 x² + 13x + 12 =0 12 12 1 = (x + 12) (x + 1) =0 13 2 2 = (x + 6) (x + 1) =0 Multiply by 2 to 2 get rid of the fraction = (x + 6) (2x + 1) =0 So your answers are -6 and -1/2
  • 10.
    Practice: Solve using Bottom’s Up/Barrowing Method • 2x2 – 19x + 24 (x-8)(2x-3)
  • 11.
    Factor by Grouping 2x² – 7x – 15 =0 -30 2x² – 10x + 3x – 15 =0 -10 3 -7 Note: you are on the right 2x(x – 5) + 3(x – 5) =0 track because you have (x-5) in both (2x + 3)(x – 5)=0 parenthesis So your answers are -3/2 and 5
  • 12.
    Practice: Factor byGrouping 3x2 + 7x - 20 (x+4)(3x-5)
  • 13.
    SHORTCUTS • a2 +2ab + b2 (a+b)2 Example: 25x2 + 90x + 81 (5x + 9)2 • a2 - 2ab + b2 (a - b)2 Example: 9x2 – 42x + 49 (3x – 7)2 • a2 - b2 (a+b)(a - b) Example: x2 – 64 (x + 8)(x – 8)
  • 14.
    Practice Problems: Solveusing any method Solutions: • 3x2 – 16x – 12 a)(x-6)(3x+2) • 4x2 + 5x – 6 • 4x2 – 49 c) (x+2)(4x-3) • 2x2 + 11X + 12 d)(2x+7)(2x-7) e)(x+4)(2x+3)