SOLUTION: please prove: sin8(x)=2sin4(x)cos4(x)

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Question 237241: please prove: sin8(x)=2sin4(x)cos4(x)
Answer by rapaljer(4671) About Me  (Show Source):
You can put this solution on YOUR website!
You are probably familiar with the double angle formula for sines:
sin%282y%29+=+2%2A%28+siny%29%2A%28cosy%29

In this case, you have sin%288x%29, so use the above formula where you substitute 4x in place of the y:
sin%282%2A4x%29+=+2+%2A%28sin4x%29%2A%28cos4x%29
sin%288x+%29=+2+%2A%28sin4x%29%2A%28cos4x%29

Dr. Robert J. Rapalje, Retired
Seminole State College of Florida
Altamonte Springs Campus