AP Calculus AB: 5.7 Using the Second Derivative Test to  Determine Extrema – Exam Style questions with Answer- MCQ

Question

A I only

B ii ONLY

C III only

D I and III only

▶️Answer/Explanation

Ans:B

 Since f(1)=0 and f′′(1)<0, there is a relative maximum at x=1 by the Second Derivative Test. Therefore, statement II is true.Statement I is false since there is a relative maximum at

x=1

.Statement III is false since f(4)=0 and f′′(4)>0 imply that there is a relative minimum at x=4 by the Second Derivative Test, not a relative maximum.

Question

Let

f

 be a twice-differentiable function. Selected values of f

 and f

 are shown in the table above. Which of the following statements are true?

 

I. f

 has neither a relative minimum nor a relative maximum at x=2.

II. f has a relative maximum x=2.

III. f has a relative maximum x=8.

A I only

B II only

C III only 

D I and III only

▶️Answer/Explanation

Ans:B

 Since f(2)=0 and f′′(2)<0, there is a relative maximum at x=2 by the Second Derivative Test. Therefore, statement II is true.Statement I is false since there is a relative maximum at 

x=2

.Statement III is false since f(8)=0and f′′(8)>0 implies that there is a relative minimum at x=8 by the Second Derivative Test, not a relative maximum.

Question

The derivative of
\(f(x)=\frac{x^{4}}{3}-\frac{x^{5}}{5}\) attains its maximum value at x =

(A) –1                                  (B) 0                                          (C) 1                          (D)\(-\frac{1}{8} \)                          (E)\(-\frac{1}{2}\)

▶️Answer/Explanation

Ans:C

f”>0 for x <1 and f ‘ >0 for x>1 ⇒ f’ has its maximum at x = 1.

Question

An equation of the line tangent to  \(y=x^{3}+3x^{2}+2\) at its point of inflection is

(A)y=-6x-6                          (B)y=-3x+1                      (C)y=2x+10                       (D)y=3x-1                              (E)y=4x+1

▶️Answer/Explanation

Ans:E

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