cos3x=4cos^3 x-3cosx (x after ^3 is not rooted...)

C

clementine

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Jun 21, 2006
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8
Well, there. I have a feeling that I shouldn't change anything into sines and such since all of them are already in cos... but I have no dern clue what I'm workin' here. Any help with solving this identity??? Any takers?
 
Expand cos(3x) = cos(2x+x)
Then, expand the cos(2x) = cos(x+x) and sin(2x) = sin(x+x)
Then, see what you get.

These are just equations. You can't break them. Just give something a shot and see what drops out.
 
??

cos(x+x+x) + sin(x+x)=4cos^3 x-3cosx

well, now I'm curious. See, I only started this account to help my brother. But, I don't get it. Where'd the sin come from. Now, I really wanna know...not just help a sibling...
 
Re: ??

clementine said:
cos(x+x+x) + sin(x+x)=4cos^3 x-3cosx

well, now I'm curious. See, I only started this account to help my brother. But, I don't get it. Where'd the sin come from. Now, I really wanna know...not just help a sibling...
Click to expand...
We don't have ANY good experience working through an intermediary.

cos(2x+x) = cos(2x)cos(x) - sin(2x)sin(x)

That's where the sin(x) came from.
 
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