# Cos-Derivative

posted by
**Mark**
.

y= (cos^3 x) (cos 3x)

I got -3 sin(3x) cos^3x - 3 sin(x) cos (3x) cos^2 (x) using the product rule

Is this right? Thanks.

posted by
**Mark**
.

y= (cos^3 x) (cos 3x)

I got -3 sin(3x) cos^3x - 3 sin(x) cos (3x) cos^2 (x) using the product rule

Is this right? Thanks.