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i have a problem with composed with two questions:

first i havr to prove that

cos(3x)=cos(x).(4cos^2(x) - 3)

okay, for this one, I was able to prove it; then the second question came, saying:

what is sin(pi/10) and cos(pi/10)

i dont know how to do that, but it should be related to the question before, how!? i don't know!

anyone with something to say ... ??

thanks

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# Homework Help: How to prove this trig equation

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