Question

find x when f(x)=1

f(x)= x^2+x-12/x^2-4

Answer 1

You must use parentheses or I can not tell what you mean. I have no idea what your other problem is about but can guess this one is:
f(x) = (x^2 + x - 12) / (x^2-4) = 1
or
x^2 + x - 12 = x^2 - 4
x - 8 = 0
x = 8