# How can I verify this identity?

See file.
LVL 3
###### Who is Participating?
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

Commented:
Checking it at several values of x could lend some validity to it.
0
Author Commented:
0
Commented:
Or verify the double angle tangent identity here:
http://en.wikipedia.org/wiki/Proofs_of_trigonometric_identities#Double-angle_identities
and apply it twice
0
Commented:
If you let   y =2x , then   tan(4x) = tan(2y)

If you apply the the double angle formula as ozo has suggested, you will get an expression in terms of   tan(y) = tan(2x)

If you can apply the double angle formula again, you will get a slightly messy expression which can be simplified to the given form.

This is a slightly more involved three or four step proof.
0

Experts Exchange Solution brought to you by