Maxima and minima: Critical points where f'(x) = 0 or undefined. First derivative test: (1) If f' changes from + to - at c, then f(c) is local maximum; (2) If f' changes from - to + at c, then f(c) is local minimum; (3) If f' doesn't change sign, neither. Second derivative test: If f'(c) = 0: (1) f''(c) > 0 → local minimum; (2) f''(c) < 0 → local maximum; (3) f''(c) = 0 → inconclusive. Example: f(x) = x³ - 3x. f'(x) = 3x² - 3 = 0 → x = ±1. f''(x) = 6x. At x=-1: f''(-1) = -6 < 0 (max, f(-1)=2). At x=1: f''(1) = 6 > 0 (min, f(1)=-2). Exam tip: Find critical points. Use appropriate test. Interpret in context (profits, costs).