How do you find the value of $cos(2 tan ^-1 x)$ ?

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Answer 1 · 2015-10-22T15:11:21

Substitute the value of $x$ for $x$ ; evaluate $tan^(-1)(x)$ ; multiply by 2; evaluate the $cos$ of the result.

Perhaps you meant:
"Find the value of $x$ for which $cos(2tan^(-1)(x))=0$ "
or something similar (???)

otherwise we have a question like:
"Find the value of $x+2$ "

How do you find the value of cos(2 tan ^-1 x)cos(2 tan ^-1 x)?