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

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Answer 1 · 2015-12-27T07:27:16

#frac{dy}{dx} = -2sin(2x)#

Let #u = 2x#

#frac{du}{dx} = 2#

#frac{dy}{dx} = frac{d}{dx}(cos(2x))#

#= frac{d}{dx}(cos(u))#

#= frac{d}{du}(cos(u))*frac{du}{dx}#

#= (-sin(u))*(2)#

#= -2sin(2x)#