What is the derivative of $f(x)=cosx*cos2x$ ?

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Answer 1 · 2015-11-19T16:14:18

$-sinxcos2x-2sin2xcosx$

Also, find the derivatives of the two terms first.

$d/dx[cosx]=-sinx$
$d/dx[cos2x]=-2sin2x$

$d/dx[cosx*cos2x]=-sinxcos2x-2sin2xcosx$

What is the derivative of f(x)=cosx*cos2xf(x)=cosx*cos2x?