Let f(x)=arctan(x)+arctan(1/x)f(x) = \arctan(x) + \arctan(1/x)f(x)=arctan(x)+arctan(1/x) for x>0x > 0x>0. What is f′(x)f'(x)f′(x)?
21+x2\frac{2}{1+x^2}1+x22
111
000
11+x2\frac{1}{1+x^2}1+x21