For f(x)=x2−1x2+1f(x) = \frac{x^2-1}{x^2+1}f(x)=x2+1x2−1, find the range
All real numbers
(−∞,1)(-\infty, 1)(−∞,1)
[−1,1)[-1, 1)[−1,1)
(0,1)(0, 1)(0,1)