How would I evaluate cos(2 arctan(2))?

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- Oct 16th 2011, 05:43 PMManniInverse Trig Ratios
How would I evaluate cos(2 arctan(2))?

- Oct 16th 2011, 06:40 PMSammySRe: Inverse Trig Ratios
Use

Then can you find - Oct 16th 2011, 06:50 PMManniRe: Inverse Trig Ratios
Do you mind working it out for me?

- Oct 16th 2011, 08:08 PMSorobanRe: Inverse Trig Ratios
Hello, Manni!

Quote:

Let

Then: .

That is, is in a right triangle with

. . Hence: .

We have: .

- Oct 16th 2011, 09:13 PMManniRe: Inverse Trig Ratios
Thank you! This clarified everything!