I need to simplify cos(arctan(x)). I did trig a few years ago and can't remember basic stuff like this.
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Originally Posted by eniuqvw I need to simplify cos(arctan(x)). $\displaystyle \phi = \arctan (x)\, \Rightarrow \,\tan (\phi ) = x = \frac{x} {1}\, \Rightarrow \,\cos (\phi ) = \frac{1} {{\sqrt {1 + x^2 } }}$
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