Types of Stationary Points
Gradients Near Stationary Points
Another definition of stationary points (called critical points in movie).
https://www.khanacademy.org/math/differential-calculus/derivative_applications/critical_points_graphing/v/minima-maxima-and-critical-points
https://www.khanacademy.org/math/differential-calculus/derivative_applications/critical_points_graphing/v/minima-maxima-and-critical-points