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# Section 1.8 solving add sub equations (math)

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### Section 1.8 solving add sub equations (math)

1. 1. Section 1.8 Solving Addition and Subtraction Equations
2. 2. Which word do you think “Equation” has a connection to? Equillateral? Equator? Equal? Equity?
3. 3. YOU’RE CORRECT!
4. 4. An equation is a mathematical sentence that contains an equal sign .
5. 5. The part on the left side of the equal sign has the same value as the part on the right side. One or both sides may contain a variable.
6. 6. What is a variable? A. A number that changes constantly . B. A letter or symbol that stands for a number. C. A number that varies as you move away from zero.
7. 7. YOU’RE CORRECT!
8. 8. A variable is a letter or symbol that stands for a number.
9. 9. To solve an equation, you must find what the variable represents so that the two parts are equal.
10. 11. Equations are like balance scales. In order to keep a scale balanced you must have the same amount of weight on both sides.
11. 12. If I took one block away from the left side, what would I have to do to keep the scale from tipping?
12. 13. If I added 6 more apples to the right side, how could I keep the scale from tipping?
13. 14. To keep an equation equal, we must do exactly the same thing to each side of the equation . If we add a number to one side, we must add that same number to the other side and vice versa.
14. 15. Addition and subtraction are called “ opposite operations ” because they can ‘undo’ each other.
15. 16. What are the other two opposite operations?
16. 17. Multiplication and division are opposite operations, too!
17. 18. for Solving Addition and Subtraction Equations Rules
18. 19. <ul><li>1. Look to see what side the variable is on. </li></ul>
19. 20. <ul><li>2. Decide what operation is being shown. </li></ul>
20. 21. <ul><li>3. Do the opposite of that operation to both sides. </li></ul>
21. 22. <ul><li>4. Write what number the variable stands for (ex: a = 2) . </li></ul>
22. 23. <ul><li>5. Check the solution by “plugging” the number back into the equation to see if the sides are equal. </li></ul>
23. 24. Example 1 <ul><li>m + 18 = 34 Look for variable </li></ul><ul><li>-18 -18 Do the opposite </li></ul><ul><li>m = 16 Write what m is </li></ul><ul><li>m + 18 = 34 </li></ul><ul><li>16 + 18 = 34 Plug in m </li></ul><ul><li>34 = 34 Solution is correct! </li></ul>
24. 25. If you check your solution and you do not come out with the same numbers, then your solution is not correct. Therefore, you must rework the problem.
25. 26. Always check your answers to equations. It is the only way to make sure you get a problem correct. Why miss a problem when you can get all of them correct ?
26. 27. Example 2 <ul><li>68 = y + 43 Look for variable </li></ul><ul><li>-43 -43 Do the opposite </li></ul><ul><li>25 = y Write what y is </li></ul><ul><li>68 = y + 43 </li></ul><ul><li>68 = 25 + 43 Plug in y </li></ul><ul><li>68 = 68 Solution is correct! </li></ul>
27. 28. Example 3 <ul><li>t - 14 = 22 Look for variable </li></ul><ul><li>+ 14 +14 Do the opposite </li></ul><ul><li>t = 36 Write what t is </li></ul><ul><li>t - 14 = 22 </li></ul><ul><li>36 - 14 = 22 Plug in t </li></ul><ul><li>22 = 22 Solution is correct! </li></ul>
28. 29. Try These... <ul><li>1. r + 5 = 18 </li></ul><ul><li>2. m - 26 = 59 </li></ul><ul><li>3. 102 = x - 15 </li></ul><ul><li>4. a + 39 = 56 </li></ul><ul><li>r = 13 </li></ul><ul><li>m = 85 </li></ul><ul><li>117 = x </li></ul><ul><li>a = 17 </li></ul>
29. 30. Let’s do Checking for Understanding Page 47 # 4 - 9
30. 31. Prediction: You will show all of the steps (including checking) as you have been shown today or credit will not be given for your homework.
31. 32. Are there any questions about solving addition or subtraction equations?
32. 33. Homework: Page 48 12-34 even Don’t forget to check your solution!