Unsure about solution to integration problem..

[f0rked]

Hi everyone! I'm trying to work through this equation here:

I'm not sure if I've got it right, however.

I've gotten this, but I don't know if its okay to simply take Q/2PiL out of the integral on the left?

Could anyone tell me if I've got it right/wrong? I would be very grateful!

Thanks!

 

[Dr. Flim-Flam]

Looks find to me.