Which equation is an identity?

A. 7m - 2 = 8m + 4 - m

B. 8y + 9 = 8y - 3

C. 11 - (2v + 3) = - 2v - 8

D. 5w + 8 - w = 6w - 2 (w - 4)

An identity is obtained when you substitute any value of x to an equation, both sides will give out the same answer. A trial-and-error method is best used for questions like these. The method is shown below:

Let: 1 = m = y = v = w

A. 7m - 2 = 8m + 4 - m

7 (1) - 2 = 8 (1) + 4 - (1)

5 = / = 11

B. 8y + 9 = 8y - 3

8 (1) + 9 = 8 (1) - 3

17 = / = 5

C. 11 - (2v + 3) = - 2v - 8

11 - (2 (1) + 3) = - 2 (1) - 8

6 = / = - 10

D. 5w + 8 - w = 6w - 2 (w - 4)

5 (1) + 8 - 1 = 6 (1) - 2 (1 - 4)

12 = 12

Therefore, the choice D is the identity.