Find and classify the critical points of $f(x, y) = -x^2y + 6x^2 + 2y^2 - 20y + 50$.
For each type of behavior, enter a list of ordered pairs where the maximum/minimum/saddle point occurs.
If there are no points where the behavior occurs, enter "DNE"
f(x, y) has a local maximum at
f(x, y) has a local minimum at
f(x, y) has a saddle point at