PROVE: sin4x = 2sin2xcos2x
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Originally Posted by chopstixdcb PROVE: sin4x = 2sin2xcos2x Use the fact that 4x=2x+2x and that sin(a+b)=sin(a)cos(b)+cos(a)sin(b).
Or, if you already know that sin(2x)= 2 sin(x)cos(x), just replace x with 2x.
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