Question

# For a function of two variables, describe critical point.

Derivatives
For a function of two variables, describe critical point.

1.$$\displaystyle\triangledown f{{\left({a},{b}\right)}}={0}$$ (this is equivalent to saying that $$\displaystyle{{f}_{{{x}}}{\left({a},{b}\right)}}={0}\ {\quad\text{and}\quad}\ {{f}_{{{y}}}{\left({a},{b}\right)}}={0}{)}$$,
2.$$\displaystyle{{f}_{{{x}}}{\left({a},{b}\right)}}\ {\quad\text{or}\quad}\ {{f}_{{{y}}}{\left({a},{b}\right)}}$$ doesn’t exist