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

##### 1 Answer

Jan 5, 2016

#### Explanation:

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