How do find the derivative of $y = cos^2(x)$ ?

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Answer 1 · 2015-09-15T02:55:46

First of all $y=cos^2x=(cosx)^2$

Hence

$y'=2cosx*(cosx)'=2cosx*(-sinx)=-2cosx*sinx=-sin2x$

Another way is

$y=cos^2x=1/2(1+cos2x)$

Hence

$y'=1/2*(-sin2x *(2x)')=-sin2x$

How do find the derivative of y = cos^2(x) y = cos^2(x)?