# Simplify cos(2arctan(x))

by steph124355
Tags: cos2arctanx, simplify
 Sci Advisor HW Helper P: 4,300 You did the simplification correctly, but usually we give the domain in terms of x, not its square. And why is $x^2$ not allowed to be zero? $x^2$ can never be negative, but how about x? As for the simplification, in such cases you could try to do some factorization (e.g. $x^2 - 1 = (x + 1)(x - 1)$) and cancel something in the top and bottom, though you'll find in this case that such an approach doesn't help you very much.