Confused about this solution manual approach-link included

[pyroknife]

Homework Statement

http://kellykemnitz.com/college/Spring 2011/PHYS 214/PhysicsSolution/Chap 22 SM.pdf
Problem #22
They chose dq to be in the 1st quadrant, what if I chose dq in any of the other quadrants? Wouldn't that be right also? But that would change the signs of the answer.

 

[Delphi51]

Yes, you should be able to draw the diagram in any quadrant. But you will still integrate from 0 to 2 pi (around the whole circle), so you'll get the same answer.