Which one?
A. B. C. Or D.

D

Step-by-step explanation:

Given

a² - 1 = 0 ( add 1 to both sides )

a² = 1 ( take the square root of both sides )

a = ± = ± 1

solution is { 1, - 1 } → D

D) {1, -1}

Step-by-step explanation:

Please share the instructions for this problem:  Solve a^2 - 1 = 0, or find the roots of a^2 - 1 = 0.

Answer D is correct.  Try substituting 1 for a, and then -1 for a.  In both cases the given equation is true.

answer: you need to organize this better it does not make sense.

step-by-step explanation: ?

step-by-step explanation:

what is the figure? attach a picture.