Minima, maxima and critical points.Authored by: Khan Academy.Located at: https://www.khanacademy.org/math/calculus-all-old/derivative-applications-calc/critical-points-calc/v/minima-maxima-and-critical-points.License: CC BY-NC-SA: Attribution-NonCommercial-ShareAlike.
Testing critical points for local extrema.Authored by: Khan Academy.Located at: https://www.khanacademy.org/math/ap-calculus-ab/ab-diff-analytical-applications-new/ab-5-4/v/testing-critical-points-for-local-extrema.License: CC BY-NC-SA: Attribution-NonCommercial-ShareAlike.