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Trigometric Proof 
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#1
Jun1211, 09:52 AM

P: 1

I am having trouble proving the following trigonometric equation:
cosx + cos3x +cos5x = sin6x/2sinx Any help would be appreciated 


#2
Jun1211, 10:15 AM

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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 & multipleangle identities).



#3
Jun1211, 02:40 PM

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Thanks
P: 10,661

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


#4
Jun1211, 03:45 PM

P: 1,035

Trigometric Proof
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. 


#5
Jun1711, 01:26 PM

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P: 10,661

Try to write both sides in terms of cos(3x) and cos(x), using the addition rules. (x=3x2x, 5x=3x+2x, 6x=2*(3x) ).
ehild 


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