AP Calculus AB Concavity and the Second Derivative Test with Point Values (PDF)

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This concavity test for AP Calculus AB covers concavity and the second derivative (Common Core AP CALC AB 5.7, AP CALC AB 5.8, AP CALC AB 5.9), with a free PDF to print.

This test checks concavity, inflection points, the Second Derivative Test and connecting the graphs of f, f prime and f double prime (AP Calculus AB, 5.7, 5.8, 5.9). It has 8 questions worth 20 points in total. Allow 45 minutes, work without notes, and show all work, since justification earns points on the AP exam.

Time and points

About this test
  • Grade: AP Calculus AB
  • Chapter: Concavity and the Second Derivative
  • Standards: AP CALC AB 5.7, AP CALC AB 5.8, AP CALC AB 5.9
  • Time: 45 minutes
  • Total: 20 points

Concavity test: questions

Question 1 – Concavity intervals [2 pts]

Find the intervals where \(f(x)=x^{4}-12x^{2}+5\) is concave up and concave down.

Question 2 – Inflection point [3 pts]

-4-3-2-1123456-30-20-101020xyinflection (1, -10)
Graph of f(x) = x³ − 3x² − 9x + 1.

Find the inflection point of \(f(x)=x^{3}-3x^{2}-9x+1\) and justify with the sign of \(f^{\prime\prime}\).

Question 3 – Second derivative test [2 pts]

Use the Second Derivative Test to classify the critical numbers of \(f(x)=x^{3}-3x+2\).

Question 4 – Graph of the derivative [3 pts]

-3-2-1123-4-3-2-11234xf’
The graph of f′ (not f).

The graph shows \(f^{\prime}(x)=\frac{x(x-2)(x+2)}{2}\). (a) Where does \(f\) have relative extrema? (1 point) (b) On which intervals is \(f\) concave up? (1 point) (c) Find the \(x\)-coordinates of the inflection points. (1 point)

Question 5 – Reading a summary table [3 pts]

interval(-∞, 1)(1, 3)(3, ∞)f′+−−f″−−+
Signs of f′ and f″ for a continuous function f.

Use the table. (a) Where is \(f\) increasing? (1 point) (b) Where does \(f\) have a relative maximum? (1 point) (c) Where is there an inflection point? (1 point)

Question 6 – Justify a statement [2 pts]

Jamal says that \(g(x)=x^{4}\) has an inflection point at \(x=0\) because \(g^{\prime\prime}(0)=0\). Is he correct? Explain.

Question 7 – Fastest growth [3 pts]

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The rate V′(t).

The volume of water in a reservoir in thousands of gallons is \(V(t)=-t^{3}+12t^{2}\) for \(0\le t\le 9\) days. (a) Find \(V^{\prime}(t)\) and \(V^{\prime\prime}(t)\). (1 point) (b) When does the volume increase fastest? (1 point) (c) What is that maximum rate? (1 point)

Question 8 – Finding constants [2 pts]

The function \(f(x)=x^{3}+ax^{2}+bx\) has an inflection point at \(x=1\) and a relative minimum at \(x=3\). Find \(a\) and \(b\).

See the solutions: Concavity and the Second Derivative test solutions

Key facts behind this concavity test

Key facts
  • A positive f″ means concave up (slope increasing); a negative f″ means concave down (slope decreasing).
  • An inflection point needs a change in the sign of f″, not just f″ = 0.
  • Second Derivative Test: f′(c) = 0 and a positive f″(c) gives a relative minimum; a negative f″(c) gives a maximum.
  • If f″(c) = 0 the test fails; use the First Derivative Test.

How to use this concavity test

Time yourself: the test is designed for an average student in 45 minutes. Answer the questions you are sure of first, then come back to the longer ones and check your units.

All AP Calculus AB chapters: AP Calculus AB math.

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AP Calculus AB Concavity and the Second Derivative Test with Point Values

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