Problem

Given ,

find and classify the extremes.

Attempt

I have a problem with the second derivatives. That expression would be huge. Have I been thinking wrong? Here's my calculations:

* 2012-09-07 15.15.06.jpg

* 2012-09-07 15.15.15.jpg

* 2012-09-07 15.15.21.jpg

The method I use to classify is:

When is positive, we have a min or maximum. If A>0 then it's a min, if A<0 it's a maximum. If is negative, then we have a saddle point.