$\displaystyle z=e^{-(x^2+y^2)}$

find the maximum slope and give answer in degrees

I believe that since this is a paraboloid and is symmetrical that I can treat it with only the z and x axis. So I take the second order partial derivative with respect to x and get

$\displaystyle 4xe^{-(x^2+y^2)}-2e^{-(x^2+y^2)}$ and equate it with 0. After that I have no clue how to proceed.