# Homework Help: Fourier series 3

1. Jun 15, 2012

### robertjford80

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

3. The attempt at a solution

I don't see why the n is in the denominator

2. Jun 15, 2012

### algebrat

reverse chain rule. What's the derivative of $\frac{\sin(nx)}{n}?$

If that doesn't make sense, then...

you could use u-substitution to avoid going backwards.

If you don't know u-substitution, that can be part of the problem.

3. Jun 15, 2012

### robertjford80

thanks, got it

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