# Trigometric Proof

by es801
Tags: algebra, proof, trigonometry
 P: 1 I am having trouble proving the following trigonometric equation: cosx + cos3x +cos5x = sin6x/2sinx Any help would be appreciated
 HW Helper P: 1,347 You'll need to show us your attempt before we can help you. I assume that you are familiar with the trigonometric identities (particularly, the sum/difference & multiple-angle identities).
 HW Helper Thanks P: 10,661 Are you familiar with complex numbers and Euler's formula? ehild
P: 1,035
Trigometric Proof

 Quote by ehild Are you familiar with complex numbers and Euler's formula? ehild
They don't teach those in general trigonometry. Though that would work (as it usually does).

Since this is in terms of x, I would try to use the identity (sin(x+x))= ... to get the whole thing in terms of single variables. For example sin(5x) is really sin(4x+x) which can expand, and then sin(3x+1) expands out and so on. Then it should be easy to simplify.
 HW Helper Thanks P: 10,661 Try to write both sides in terms of cos(3x) and cos(x), using the addition rules. (x=3x-2x, 5x=3x+2x, 6x=2*(3x) ). ehild

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