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

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Answer 1 · 2016-01-05T21:21:43

# dy/dx = -2sin2x #

what we have here is a function 2x inside another function cos .

This is known as a function of a function.

If we differentiate cosx we get - sinx

when we differentiate cos2x we get - sin2x but then have to differentiate 2x.

This can be written as y = cos2x

# rArr dy/dx = - sin2x . d/dx (2x )= - sin2x . 2 #

#rArr dy/dx = -2sin2x #