A function has critical points at all points where or is not differentiable. A function has critical points where the gradient or or the partial derivative is not defined.
Critical Point
See also
Fixed Point, Inflection Point, Only Critical Point in Town Test, Stationary Point Explore this topic in the MathWorld classroomExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Critical Point." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/CriticalPoint.html