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Solving Equations by Adding or Subtracting Objective: Solve equations using the addition and subtraction properties of equalities.

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Subtraction Property of Equality For any numbers a, b, and c, if a =b, then a – c = b – c.

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Example 1 Solve x + 9 = 5. Check your solution.

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Example 1 Solve x + 9 = 5. Check your solution. x + 9 = 5 -9 -9 Subtract 9 from each side

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Example 1 Solve x + 9 = 5. Check your solution. x + 9 = 5 – 9 - 9 Subtract 9 from each side. x = -4 Check: x + 9 = 5

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Example 1 Solve x + 9 = 5. Check your solution. x + 9 = 5 – 9 - 9 Subtract 9 from each side. x = -4 Check: x + 9 = 5 -4 + 9 ? 5Replace x with -4.

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Example 1 Solve x + 9 = 5. Check your solution. x + 9 = 5 – 9 - 9 Subtract 9 from each side. x = -4 Check: x + 9 = 5 -4 + 9 ? 5Replace x with -4. 5 = 5 The solution is x = -4.

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Addition Property of Equality For any numbers a, b, and c, if a =b, then a + c = b + c.

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Example 2 Solve x - 4 = -1. Check your solution.

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Example 2 Solve x - 4 = -1. Check your solution. x – 4 = -1 + 4 + 4 Add 4 to each side.

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Example 2 Solve x - 4 = -1. Check your solution. x – 4 = -1 + 4 + 4 Add 4 to each side. x = 3

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Example 2 Solve x - 4 = -1. Check your solution. x – 4 = -1 + 4 + 4 Add 4 to each side. x = 3 Check: x - 4 = -1

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Example 2 Solve x - 4 = -1. Check your solution. x – 4 = -1 + 4 + 4 Add 4 to each side. x = 3 Check: x - 4 = -1 3 - 4 ? -1 Replace x with 3 -1 = -1 The solution is x = 3

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1) Solve r + 16 = -7 Think of this equation as a balance scale. Whatever you do to one side has to be done to the other to keep it balanced!

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1) Solve r + 16 = -7 To solve, you must get the variable by itself. What number is on the same side as r? 16 To get r by itself, we must undo the “add 16”. What is the opposite of addition? Subtract 16

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- 16 -16 r = -23 -23 + 16 = -7 1) Solve r + 16 = -7 1.Draw “the river” to separate the equation into 2 sides 2.Subtract 16 from both sides 3.Simplify vertically 4.Check your answer by substituting your answer back into the problem

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2) Solve x + 2 = -3 Get the variable by itself. What is your first step? 1.Add 2 to both sides 2.Subtract 2 from both sides 3.Add 3 to both sides 4.Subtract 3 from both sides Answer Now

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2) Solve x + 2 = -3 - 2 - 2 x = -5 -5 + 2 = -3 1.Draw “the river” to separate the equation into 2 sides 2.Subtract 2 from both sides 3.Simplify vertically 4.Check your answer by substituting your answer back into the problem On homework and tests, be sure to check your work!! There is no reason why you should miss a problem!

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3) Solve 8 = m - 3 1.m = 5 2.m = 11 3.m = 24 4.m = 8/3 Answer Now

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3) Solve 8 = m - 3 + 3+ 3 11= m 8 = 11 - 3 1.Draw “the river” to separate the equation into 2 sides 2.Add 3 to both sides 3.Simplify vertically 4.Check your answer by substituting your answer back into the problem

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When solving equations, we want to eliminate double signs. y + (-3) = 8 is rewritten as y – 3 = 8 p – (-5) = 6 is rewritten as p + 5 = 6 As a general rule, replace “+ (- )” with “–” and “– (- )” with “+”. This will make things less confusing in the future!

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4) Solve y + (-3) = 7 y – 3 = 7 + 3 +3 y = 10 10 + (-3) = 7 1.Draw “the river” to separate the equation into 2 sides 2.Eliminate the double sign 3.Add 3 to both sides 4.Simplify vertically 5.Check your answer by substituting your answer back into the problem

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Assignment P. 112 #4-9, 16-21, 30, 33

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