# Definite integral using contour integration.

• Oct 18th 2011, 10:37 PM
mopen
Definite integral using contour integration.
Hi

i need help in solving this integral for this specific integration limit:

int (0) to (pi/2) {cos (2 theta)/(cos(theta)-x)}dtheta abs (x)<1

mopen
• Oct 18th 2011, 11:01 PM
FernandoRevilla
Re: i need help solving this integral.
If the problem has been proposed in the context of complex variable, use the substitution $z=e^{i\theta}$ .
• Oct 18th 2011, 11:23 PM
mopen
Re: i need help solving this integral.
yes, i did that but the problem is that i got imaginary part of the solution, but i think the integral should be real.
• Oct 19th 2011, 12:29 AM
FernandoRevilla
Re: i need help solving this integral.
Quote:

Originally Posted by mopen
yes, i did that but the problem is that i got imaginary part of the solution, but i think the integral should be real.

Indeed, the solution must be real. Please, show your work an we can check it.
• Oct 19th 2011, 09:21 AM
mopen
Re: Definite integral using contour integration.
Hi
i have attached two different solution for the problem. from the first one i got unexpected results at low x and at the second one i got imaginary part of the solution.

So any help with the problem!

thanks

mopen