Here is the question I have a problem with

http://www.flickr.com/photos/venom104/6324190550/

The actual question is doubleintegral(R) arctan(y/x) where R = {(x,y) | 1 <= x^2 + x^y <=4, 0 <= y <= x}

My question is on STEP two Lines 2/3; on line 3 they have the double integral of arctan(tan theta), meaning going from step 2 to step 3 they DIVIDED BY A VARIABLE (remember we integrate with respect to r first in using polar coordinates).

So if you divide by a variable you need to restrict the domain by excluding r = 0, so the answer is only valid for those answers were r isn't zero.

Am I correct and is this solution sort of wrong?

mohanrao d, thank you, I didn't realize that. You will get best answer.