Question

What is the solution set of 4x 2 - 36 = 0? A.{-3} B.{3} C.{-3, 3}

Answer 1

It is short work to check the answer choices.
  4*3² -36 = 0 . . . . yes, so +3 is a solution
  4*(-3)² -36 = 0 . . . . yes, so -3 is a solution

The appropriate choice is ...
  C. {-3, 3}

Answer 2

4x^2 - 36 = 0
4x^2 = 36
x^2 = 9
x = 3 or -3
the answer is C