Find the derivative of f(x)=arctan(x+11−x)f(x) = \arctan\left(\frac{x+1}{1-x}\right)f(x)=arctan(1−xx+1) for x≠1x \neq 1x=1.
11+x2\frac{1}{1+x^2}1+x21
1x2\frac{1}{x^2}x21
111
−1-1−1