- #51

ehild

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Sammy is the greatest!Just need to get cos(3x) in terms of cos(x):

##\cos(3x)=4\cos^3(x)-3\cos(x)##The derivative of the numerator is then ##\ 12\sin^3(x)\ .##

The derivative of the denominator then has a factor of ##\ \sin^3(2x)\ ## which is easily reduced.

##\sin^3(x)\ ## in both numerator & denominator cancel. The answer is readily at hand.