# Homework Help: Derivative of a trig function/chain rule

1. Apr 8, 2009

### andrew.c

1. The problem statement, all variables and given/known data

Differentiate $$sin^3 2x$$

2. Relevant equations

Chain rule.

3. The attempt at a solution

I just need to see if I got the answer right, there aren't any solutions available for this paper, and I need it for the next parts of a question...

I got...
\begin{align*} = (sin 2x)^3\\ differentiate\\ = 3 (sin 2x)^2 (2 cos 2x)\\ = 6 cos 2x sin^2 2x\\ \end{align*}

?

2. Apr 8, 2009

Correct.

3. Apr 8, 2009

### andrew.c

Sweet!
Muchos gracias!

4. Apr 8, 2009

### andrew.c

Another quickie...

Is the derivative of $$y=xe^{-3x}$$ going to work out to be $$e^{-3x} (1-3x)$$ ?

5. Apr 8, 2009

### Staff: Mentor

Yes.

Also, that would be muchas gracias.

6. Apr 8, 2009