1. ## quick question

what is the derivative of cos squared of x? is it -2 sin x? thx in advance

2. Originally Posted by slapmaxwell1
what is the derivative of cos squared of x? is it -2 sin x? thx in advance
No it isn't - recall the chain rule

$\frac{d}{dx} \, cos^2(x) = -2cos(x)sin(x) = -sin(2x)$

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$\frac{d}{dx} \, cos(x^2) = -2xsin(x^2)$