Trigometric Proof

es801

I am having trouble proving the following trigonometric equation:
cosx + cos3x +cos5x = sin6x/2sinx

Any help would be appreciated

eumyang

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).

ehild

Are you familiar with complex numbers and Euler's formula?

ehild

QuarkCharmer

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.

ehild

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