According to some the sin of the Eitz HaDaas was with a Esrog tree. Through this came the curse of pain by child birth. When the lady bites the Pittum she is saying "just like I have no enjoyment now, I had no enjoyment then (at the sin of the Eitz HaDaas). Taamei HaMinhagim Likutim 68

What does biting off the Pitum have to do with Pregnancy?

  Find all local extrema of $f(x, y) = x^2 + y^2$. That is, find their locations and values.


I started this problem but when I took the first derivative I got the critical points as $(0, 0)$. Then I took the second derivative and got $x= 2$ and $y= 2$. What do i do next? Please help me. 
