Math Problem Statement

Given the graph of f(x) shown below, which of the following is NOT necessarily true about the graph of its derivative f'(x)?

Solution

To determine which statement is NOT necessarily true, we analyze the given graph of f(x)f(x) and its implications for the derivative f(x)f'(x):

Observations:

  1. f(x)f'(x) is the slope of the tangent to f(x)f(x) at any point.
  2. Key features:
    • At critical points (peaks and valleys), f(x)=0f'(x) = 0.
    • Where f(x)f(x) is increasing, f(x)>0f'(x) > 0; where f(x)f(x) is decreasing, f(x)<0f'(x) < 0.

Statements Analysis:

A. f(1)0f'(1) \approx 0:

  • At x=1x = 1, f(x)f(x) has a peak (local maximum).
  • Slope of the tangent =0= 0, so f(1)=0f'(1) = 0.
  • This is true.

B. f(2)>f(1)f'(-2) > f'(-1):

  • At x=2x = -2, the slope of the tangent is steeply negative.
  • At x=1x = -1, f(x)=0f'(x) = 0 (a critical point at the peak).
  • Hence, f(2)<f(1)f'(-2) < f'(-1), making this statement NOT true.

C. f(1.5)0f'(1.5) \approx 0:

  • At x=1.5x = 1.5, f(x)f(x) has a valley (local minimum).
  • Slope of the tangent =0= 0, so f(1.5)=0f'(1.5) = 0.
  • This is true.

D. f(0.5)4f'(0.5) \approx 4:

  • At x=0.5x = 0.5, f(x)f(x) appears to increase steeply.
  • Slope f(x)f'(x) is positive and approximately equal to 4.
  • This is true.

Conclusion:

The incorrect statement is B: f(2)>f(1)f'(-2) > f'(-1). In fact, f(2)<f(1)f'(-2) < f'(-1).

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Math Problem Analysis

Mathematical Concepts

Calculus
Graphical Interpretation of Derivatives
Critical Points

Formulas

Derivative definition: f'(x) = slope of tangent to f(x)

Theorems

Critical Points Theorem
Sign of Derivative and Monotonicity

Suitable Grade Level

Grades 11-12