Math Problem Statement

The graph of the function f is shown on the graph above. On the axes beneath, sketch a possible graph of f', the derivative of the function f. You must take into account the concavity of f, so the inflection points on f are shown as green dots.

Solution

To construct the graph of ff', the derivative of ff, from the graph of ff, follow these steps:


Key observations about ff in the graph:

  1. Critical points (where f(x)=0f'(x) = 0) occur where ff has horizontal tangents (flat slopes).
  2. Concavity changes (inflection points) occur where f(x)=0f''(x) = 0 and the concavity switches between up and down.
  3. The slope of ff tells us the value of ff' at any point.

Step-by-step observations:

  1. Identify where ff has horizontal tangents:

    • From the graph, these occur approximately at x=6x = -6, x=2x = 2, and x=7x = 7. At these points, f(x)=0f'(x) = 0, so ff' will cross the xx-axis.
  2. Determine where ff is increasing or decreasing:

    • ff is decreasing for x<6x < -6, so f(x)<0f'(x) < 0 in this region.
    • ff is increasing between x=6x = -6 and x=2x = 2, so f(x)>0f'(x) > 0 here.
    • ff decreases again between x=2x = 2 and x=7x = 7, so f(x)<0f'(x) < 0 here.
    • ff increases for x>7x > 7, so f(x)>0f'(x) > 0 in this region.
  3. Analyze concavity changes (green dots, f(x)=0f''(x) = 0):

    • The inflection points at x3x \approx -3 and x5x \approx 5 indicate that ff' has critical points (local maxima or minima) at these positions.

Sketching ff':

  • At x=6x = -6, x=2x = 2, and x=7x = 7, the graph of ff' crosses the xx-axis.
  • Between these points:
    • ff' starts negative (slopes of ff are decreasing).
    • Peaks or valleys in ff' occur at the inflection points of ff.
  • Ensure ff' reflects the changing slopes of ff:
    • Decreasing slopes mean ff' is negative.
    • Increasing slopes mean ff' is positive.

Let me know if you need further clarification or if you'd like me to summarize this into steps for sketching the graph!


Follow-up Questions:

  1. What is the significance of f(x)=0f'(x) = 0 for the graph of ff?
  2. How do inflection points of ff affect the graph of ff'?
  3. How can you determine f(x)f''(x) from the graph of ff?
  4. What does the sign of f(x)f'(x) tell you about ff?
  5. How would you sketch ff'' based on the graph of ff'?

Tip: Remember that ff' represents the slopes of ff, so interpreting changes in slopes is key to constructing ff'.

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Math Problem Analysis

Mathematical Concepts

Differentiation
Critical Points
Concavity and Inflection Points
Graphical Behavior of Derivatives

Formulas

f'(x) = slope of the tangent line at a point
f''(x) determines concavity: f''(x) > 0 for concave up, f''(x) < 0 for concave down

Theorems

The derivative at critical points (local max/min) equals zero
Inflection points occur where the second derivative f''(x) = 0

Suitable Grade Level

High School Calculus (Grades 11-12)