the question is

given f'(x) = (2x)/(x^2 - 4)^2 and f"(x) = -2(3x^2 + 4)/(x^2 - 4)^2

B) Use calculus to find all intervals on which f(x) is concave up or down and the find the x-coordinate of all inflection points, if they exist.

i've tride f"(x) is 0 when -2(3x^2 + 4) = 0 x= ... ?

f"(x) is undefined when (x^2 - 4)^2 = 0, x=2, -2

what should i do with " -2(3x^2 + 4) = 0 x= ... ? " <-- here?