Question

5) Consider the sequence of steps to solve the equation: 2(x − 4) + 5x = 9x − 10 Given ⇒ 2(x − 4) + 6x = 9x − 10 Step 1 ⇒ 2x − 8 + 6x = 9x − 10 Step 2 ⇒ 2x + 6x − 8 = 9x − 10 Step 3 ⇒ 8x − 8 = 9x − 10 Step 4 ⇒ 8x − 8x − 8 = 9x − 8x − 10 Step 5 ⇒ 0 − 8 = x − 10 Step 6 ⇒ −8 = x − 10 Step 7 ⇒ −8 + 10 = x − 10 + 10 Step 8 ⇒ 2 = x + 0 Step 9 ⇒ 2 = x Which step in solving this equation is justified by the Addition Property of Equality?

Answer 1

The answer to this question is Step 7.
                         Step 7 ⇒ −8 + 10 = x − 10 + 10
This is where 10 is being added to both sides. It is not Step 4 as that uses the Subtraction Property of Equality (which can be proved true by taking the addition of a negative number).

Answer 2

Answer: Step 7 is the answer.