rate of change?

Question

Find the minimum rate of change of f(x,y) = ln(x^2 + y^2) at the point (2, -3) and the direction in which it occurs.

Answer 1

This is max/min problem

f'(x,y) = 0 find x and y
then test using second derivative f''(x,y) .
Iff
f''(x,y)<0 then max
f''(x,y)>0 then min