I've done it, but do not know how to continue. I wanted to see the resolution step by step, with comments about what is being done, of course if you can.I am Brazilian and I'm using google translator, so what I am saying may seem a bit confusing.
Staff was trying to understand a matter of calculation. I hope someone can explain me in detail how to solve this limit using polar coordinates:
http://img36.imageshack.us/img36/2667/semttulokej.png