composite trig function simplification

• September 4th 2009, 09:52 AM
eniuqvw
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.
• September 4th 2009, 10:09 AM
Plato
Quote:

Originally Posted by eniuqvw
I need to simplify cos(arctan(x)).

$\phi = \arctan (x)\, \Rightarrow \,\tan (\phi ) = x = \frac{x}
{1}\, \Rightarrow \,\cos (\phi ) = \frac{1}
{{\sqrt {1 + x^2 } }}$