Question Detail
Question
The maximum value of the function
f(x) = x³ + 2x² - 4x + 6 occurs at which x-coordinate?
Correct Answer
Option B is the correct answer.
Detailed Explanation
To find the x-coordinate of the maximum value of the function, we follow these steps:
- Find the first derivative
f'(x):f'(x) = d/dx(x³ + 2x² - 4x + 6) = 3x² + 4x - 4 - Set the first derivative to zero to find critical points:
3x² + 4x - 4 = 0Using the quadratic formulax = (-b ± √(b² - 4ac)) / (2a):x = (-4 ± √(4² - 4(3)(-4))) / (2(3))x = (-4 ± √(16 + 48)) / 6x = (-4 ± √64) / 6x = (-4 ± 8) / 6The critical points are:x1 = (-4 + 8) / 6 = 4/6 = 2/3andx2 = (-4 - 8) / 6 = -12/6 = -2. - Find the second derivative
f''(x):f''(x) = d/dx(3x² + 4x - 4) = 6x + 4 - Use the second derivative test to classify the critical points:
- At
x = 2/3:f''(2/3) = 6(2/3) + 4 = 4 + 4 = 8. Since8 > 0,x = 2/3corresponds to a local minimum. - At
x = -2:f''(-2) = 6(-2) + 4 = -12 + 4 = -8. Since-8 < 0,x = -2corresponds to a local maximum.
- At
x = -2. Although the question asks for the "maximum value", the options provided are x-coordinates. Therefore, the x-coordinate for the maximum is -2.
Hint
Find the first derivative and set it to zero to get the critical points. Use the second derivative test to distinguish between maximum and minimum points. The x-coordinate where the second derivative is negative corresponds to a local maximum.