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Homework Statement
Hello!
I am having some trouble solving this integral by parts. I hope someone can help me.
##\int \cos(x)cos(kx) dx##
It is need for a Fourier series
Homework Equations
I am using this definition:
##\int f(x)g(x) dx = f(x)G(x)-\int f'(x)G(x) dx##
since its an even function i need to find ##a_k## and ##a_0##, I've found ##a_0## no worries about that.
The Attempt at a Solution
[/B]##\int f(x)g(x) dx = \frac{cos(x)sin(kx)}{k} - \int \frac{-sin(x)sin(kx)}{k}##
I can't remember/see the next rule of integration when having two sin functions. Or am i doing something wrong?
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