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# How can I verify this identity?

Posted on 2014-11-18
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See file.
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Question by:Computer Guy
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LVL 84

Expert Comment

ID: 40449632
Checking it at several values of x could lend some validity to it.
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Author Comment

ID: 40449643
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LVL 84

Expert Comment

ID: 40449666
Or verify the double angle tangent identity here:
http://en.wikipedia.org/wiki/Proofs_of_trigonometric_identities#Double-angle_identities
and apply it twice
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Accepted Solution

d-glitch earned 2000 total points
ID: 40450351
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.
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