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## Homework Statement

Use the contour integral

[itex]\int_{C}\frac{e^{pz}}{1+e^z}dz[/itex]

to evaluate the real integral[itex]\int^{\infty}_{- \infty}\frac{e^{px}}{1+e^x}dx[/itex]

0<p<1The contour is attached.

It is a closed rectangle in the positive half of the complex plane. It height is 2i∏.

## Homework Equations

[itex]\oint f(z)dz = 2 \pi i \sum Res[f(z)] [/itex]

[itex] Res[f(z=z_{0})] = (m-1)! \frac{d^{m-1}}{dz^{m-1}}(z-z_{0})^{m}f(z)|_{z=z_{0}}[/itex]

where m is the degree of the pole.

## The Attempt at a Solution

I found that there was a simple pole at z = i∏, so I must use the residue theorem to find the value of the complex integral.

[itex] Res[f(z=i \pi)] = (z-i \pi) \frac{e^{pz}}{1+e^z}|_{z=i \pi}[/itex]

In the past I've had to fiddle with the denominator to get the z-z

_{0}terms to cancel out, but in those cases it involved something nice and simple. I have no idea what to do with this equation.