MATH 121 Lecture 7: Identifying types of critical points, first and second derivative tests, global vs local optimization
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Formalize the first & second derivative test for identifying local maxima & minima. Study generalized optimization problems related to marginal rates. We have found critical pts by looking for pts on the graph where. F"(x) was undefined (although f(x) was defined) We now formalize two ways to determine if a critical pt is a local min, max, or neither. This avoids the need to sketch the graph. One way is the first derivative test: examine the sign of the derivative on opposite sides of the critical pt. Sketch f" sign left of c f" sign right of c. Find the critical points of the function f(x) = 2x3 - 9x2 + 12x + 3. Use the first derivative test to show whether each critical point is a local maximum or a local minimum. Need f"(x) = 6x2 - 18x + 12 (note: set = 0 for crit. pts) 6(x-2)(x-1) 6(x2 - 3x + 2) = 0 (x-2)(x-1) = 0.