# Math Help - composite trig function simplification

1. ## composite trig function simplification

I need to simplify cos(arctan(x)). I did trig a few years ago and can't remember basic stuff like this.

2. Originally Posted by eniuqvw
I need to simplify cos(arctan(x)).
$\phi = \arctan (x)\, \Rightarrow \,\tan (\phi ) = x = \frac{x}
{1}\, \Rightarrow \,\cos (\phi ) = \frac{1}
{{\sqrt {1 + x^2 } }}$