3.R: Chapter 3 Review Exercises

Chapter Review Exercises

True or False? Justify the answer with a proof or a counterexample.

1) Every function has a derivative.

Answer

False

2) A continuous function has a continuous derivative.

3) A continuous function has a derivative.

Answer

False

4) If a function is differentiable, it is continuous.

In exercises 5 and 6, use the limit definition of the derivative to exactly evaluate the derivative.

5) $f(x)=\sqrt{x+4}$

Answer

$f'(x) = \dfrac{1}{2\sqrt{x+4}}$

6) $f(x)=\dfrac{3}{x}$

In exercises 7 - 15, find the derivatives of the given functions.

7) $f(x)=3x^3−\dfrac{4}{x^2}$

Answer

$f'(x) = 9x^2+\frac{8}{x^3}$

9) $f(x)=(4−x^2)^3$

10) $f(x)=e^{-x^2+3}$

Answer

$f'(x) = -2x \cdot e^{-x^2+3}$

11) $f(x)=\ln(x+2)$

12) $f(x)=\dfrac{3x-7}{4x+1}$

Answer

$f'(x) = \dfrac{31}{(4x+1)^2}$

13) $f(x)=\sqrt{3x^2+2}$

14) $f(x)=\dfrac{8}{\sqrt{3x^2+4}}$

Answer

$f'(x) = \frac{-24x}{(3x^2+4)^\frac{3}{2}}$

15) $x^2y=(y+2)+4x$

In exercises 16 - 18, find the indicated derivatives of various orders.

16) Second derivative of $y=\dfrac{1}{x}$

Answer

$\dfrac{d^2y}{dx^2} = \dfrac{2}{x^3}$

17) Third derivative of $y=(3x+2)^2$

18) Second derivative of $y=\dfrac{3x}{4x+1}$

Answer

$\dfrac{d^2y}{dx^2} = \dfrac{-24}{(4x+1)^3}$

In exercises 19 and 20, find the equation of the tangent line to the following equations at the specified point.

19) $y=x^2-5x+3$ at $x=1$

20) $y=x+e^x−\dfrac{1}{x}$ at $x=1$

Answer

$y = (2+e)x−2$

In exercises 21 and 22, draw the derivative of the functions with the given graphs.

21)

22)

Answer

Questions 23 and 24 we are given the following information: The cost function for a company that manufactures widgets is given by $C(q)=100+\dfrac{2}{q}+\dfrac{q}{4}$, where $q$ is the number of widgets manufactured.

23) Find the equation for the marginal cost function, $MC(q)$.

24) Find $MC(20).$ What is the meaning of this value?

Answer

$MC(20)=0.245$. This is an approximation to the cost of the 21st widget manufactured.

Questions 25 and 26 consider the wind speeds of Hurricane Katrina, which affected New Orleans, Louisiana, in August 2005. The data are displayed in a table.

Hours after Midnight, August 26	Wind Speed (mph)
1	45
5	75
11	100
29	115
49	145
58	175
73	155
81	125
85	95
107	35

Wind Speeds of Hurricane KatrinaSource: news.nationalgeographic.com/n..._timeline.html.

25) Using the table, estimate the derivative of the wind speed at hour 39. What is the physical meaning?

26) Estimate the derivative of the wind speed at hour 83. What is the physical meaning?

Answer

$−7.5.$ The wind speed is decreasing at a rate of 7.5 mph/hr