Question Detail

MTH 102 MTH 102 Past Questions Objective Question

Question

Evaluate the minimum value of y if y = x3-3x2 +1.
Options
A 2
B 3
C -3
Correct Answer
D 7
Correct Answer

Option C is the correct answer.

Detailed Explanation

To find the minimum (or maximum) value of a function, we follow these steps:1. Find the first derivative of the function, dy/dx.2. Set dy/dx = 0 to find the critical points.3. Use the second derivative test (d2y/dx2) to determine if each critical point is a local maximum or minimum. If d2y/dx2 > 0, it's a local minimum. If d2y/dx2 < 0, it's a local maximum.4. Evaluate the original function y at the local minimum point(s).Given y = x3 - 3x2 + 1.1. dy/dx = 3x2 - 6x.2. Set dy/dx = 0: 3x2 - 6x = 0 => 3x(x - 2) = 0. The critical points are x = 0 and x = 2.3. Find the second derivative: d2y/dx2 = 6x - 6. - At x = 0: d2y/dx2 = 6(0) - 6 = -6. Since -6 < 0, x=0 corresponds to a local maximum. - At x = 2: d2y/dx2 = 6(2) - 6 = 12 - 6 = 6. Since 6 > 0, x=2 corresponds to a local minimum.4. Evaluate y at x = 2: y(2) = (2)3 - 3(2)2 + 1 = 8 - 3(4) + 1 = 8 - 12 + 1 = -3.Thus, the minimum value of y is -3.This matches option C.

Hint

Find the critical points by setting the first derivative to zero. Use the second derivative test to classify these points as local maxima or minima. Then, evaluate the function at the local minimum point(s).

Question Info