-1/4X - 7 + 9/4X + 2X

Question

Tran says that -1/4X - 7 + 9-4X + 2X is equivalent to 4X - 7. How can substituting any value for X help you determine whether Tran is correct? Is Tran correct? Use substitution to justify your answer.

Answer 1

9X/4-X/4=8X/4=2X and 2X+2X=4X, and 4X-7 is the result of the first expression which is the same as the second expression. Therefore the two expressions are equivalent and the second one is a simplified version of the first. Tran is right.

If we put X=4 into both we get -1-7+9+8=9 and 4X-7=16-7=9. So that’s correct.

If we put X=0 into both we get -7. So by substitution we show that the two expressions are equivalent.