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Multiple Choice
Suppose the graph of the derivative of a continuous function is shown and is continuous everywhere. Which of the following statements is necessarily true about the function ?
A
is always increasing wherever is negative.
B
is constant wherever is nonzero.
C
has an inflection point wherever is zero.
D
has a local maximum at any where changes from to .
Verified step by step guidance
1
Step 1: Recall the relationship between a function f and its derivative f'. The derivative f' provides information about the slope of the graph of f. Specifically, f' > 0 indicates that f is increasing, f' < 0 indicates that f is decreasing, and f' = 0 indicates a critical point where the slope is horizontal.
Step 2: Analyze the behavior of f when f' changes from positive to negative. If f' transitions from positive to negative at a point x, it means the slope of f changes from increasing to decreasing. This is a key indicator of a local maximum at x.
Step 3: Understand why the other statements are incorrect. For example, f is not always increasing wherever f' is negative; in fact, f is decreasing in such regions. Similarly, f is not constant wherever f' is nonzero; f changes based on the sign of f'. Lastly, f does not necessarily have an inflection point wherever f' is zero; inflection points are determined by changes in the concavity of f, which depend on the second derivative f''.
Step 4: Confirm that the correct statement is: 'f has a local maximum at any x where f' changes from positive to negative.' This aligns with the definition of a local maximum in terms of the derivative.
Step 5: To solidify understanding, visualize the graph of f' and consider how its behavior (positive to negative transition) corresponds to the shape of the graph of f at a local maximum.