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Multiple Choice
Suppose the graph of is shown below. At which intervals is ?
A
Where the graph of is decreasing
B
Where the graph of has a local minimum
C
Where the graph of is constant
D
Where the graph of is increasing
Verified step by step guidance
1
Step 1: Understand the relationship between f(x) and its derivative f'(x). The derivative f'(x) represents the slope of the tangent line to the graph of f(x) at any given point. When f'(x) < 0, the slope is negative, meaning the graph of f(x) is decreasing.
Step 2: Analyze the intervals where the graph of f(x) is decreasing. Look for sections of the graph where the curve is sloping downward as you move from left to right. These intervals correspond to f'(x) < 0.
Step 3: Clarify why f'(x) < 0 does not occur at local minima or constant intervals. At a local minimum, the slope of the tangent line is zero (f'(x) = 0), not negative. Similarly, when the graph is constant, the slope is zero, not negative.
Step 4: Exclude intervals where the graph of f(x) is increasing. When the graph is sloping upward, the slope of the tangent line is positive (f'(x) > 0), so these intervals do not satisfy f'(x) < 0.
Step 5: Conclude that f'(x) < 0 only occurs where the graph of f(x) is decreasing. This is the key interval to identify when solving the problem.