 # Intermediate Algebra: Functions and Graphs

## Section5.1Functions

### Investigation5.1.1.Epidemics.

A contagious disease whose spread is unchecked can devastate a confined population. For example, in the early 16th-century, Spanish troops introduced smallpox into the Aztec population in Central America, and the resulting epidemic contributed significantly to the fall of Montezuma’s empire.
Suppose that an outbreak of cholera follows severe flooding in an isolated town of 5000 people. Initially (Day 0), 40 people are infected. Every day after that, 25% of those still healthy fall ill.
1. At the beginning of the first day (Day 1), how many people are still healthy? How many will fall ill during the first day? What is the total number of people infected after the first day?
2. Check your results against the table below. Subtract the total number of infected residents from 5000 to find the number of healthy residents at the beginning of the second day. Then fill in the rest of the table for 10 days. (Round off decimal results to the nearest whole number.)
 Day Numberhealthy Newpatients Totalinfected $$0$$ $$5000$$ $$40$$ $$40$$ $$1$$ $$4960$$ $$1240$$ $$1280$$ $$2$$    $$3$$    $$4$$    $$5$$    $$6$$    $$7$$    $$8$$    $$9$$    $$10$$ 3. Use the last column of the table to plot the total number of infected residents, $$I\text{,}$$ against time, $$t\text{,}$$ on the grid. Connect your data points with a smooth curve.
4. Do the values of $$I$$ approach some largest value? Draw a dotted horizontal line at that value of $$I\text{.}$$ Will the values of $$I$$ ever exceed that value?
5. What is the first day on which at least 95% of the population is infected?
6. Look back at the table. What is happening to the number of new patients each day as time goes on? How is this phenomenon reflected in the graph? How would your graph look if the number of new patients every day were a constant?
7. Summarize your work: In your own words, describe how the number of residents infected with cholera changes with time. Include a description of your graph.

### Subsection5.1.1Definitions and Notation

We often want to predict values of one variable from the values of a related variable. For example, when a physician prescribes a drug in a certain dosage, she needs to know how long the dose will remain in the bloodstream. A sales manager needs to know how the price of his product will affect its sales. A function is a special type of relationship between variables that allows us to make such predictions.
We have already seen some examples of functions. For instance, suppose it costs $800 for flying lessons, plus$30 per hour to rent a plane. If we let $$C$$ represent the total cost for $$t$$ hours of flying lessons, then
\begin{equation*} C=800+30t ~~~~ (t\ge 0) \end{equation*}
The variable $$t$$ is called the input variable, and $$C$$ is the output variable. Given a value of the input, we can calculate the corresponding output value using the formula for the function. Thus, for example
 when $$t=\alert{0}\text{,}$$ $$C=800+30(\alert{0})=800$$ when $$t=\alert{4}\text{,}$$ $$C=800+30(\alert{4})=920$$ when $$t=\alert{10}\text{,}$$ $$C=800+30(\alert{10})=1100$$
We can display the relationship between two variables by a table or by ordered pairs. The input variable is the first component of the ordered pair, and the output variable is the second component. For the example above we have:
 $$t$$ $$C$$ $$(t,C)$$ $$0$$ $$800$$ $$(0, 800)$$ $$4$$ $$920$$ $$(4, 920)$$ $$10$$ $$1100$$ $$(10,1100)$$
Note that there can be only one value of $$C$$ for each value of $$t\text{.}$$ We say that "$$C$$ is a function of $$t\text{.}$$"

#### Definition5.1.1.Definition of Function.

A function is a relationship between two variables for which exactly one value of the output variable is determined by each value of the input variable.

#### Checkpoint5.1.2.QuickCheck 1.

What distinguishes a function from other variable relationships?
• A) There cannot be two output values for a single input value.
• B) We can display the variables as ordered pairs.
• C) The variables are related by a formula.
• D) The values of the input and output variables must be different.
$$\text{A) There ... input value.}$$
Solution.
There cannot be two output values for a single input value.

#### Example5.1.3.

1. The distance, $$d\text{,}$$ traveled by a car in 2 hours is a function of its speed, $$r\text{.}$$ If we know the speed of the car, we can determine the distance it travels by the formula $$d = r \cdot 2\text{.}$$
2. The cost of a fill-up with unleaded gasoline is a function of the number of gallons purchased. The gas pump represents the function by displaying the corresponding values of the input variable (number of gallons) and the output variable (cost).
3. Score on the Scholastic Aptitude Test (SAT) is not a function of score on an IQ test, because two people with the same score on an IQ test may score differently on the SAT; that is, a person’s score on the SAT is not uniquely determined by his or her score on an IQ test.

#### Checkpoint5.1.4.Practice 1.

1. As part of a project to improve the success rate of freshmen, the counseling department studied the grades earned by a group of students in English and algebra. Do you think that a student’s grade in algebra is a function of his or her grade in English?
• Yes
• No
Explain why or why not.
• A) Each value of $$x$$ has exactly one value of $$y$$ associated with it.
• B) Two students with the same grade English can have different grades in algebra.
• C) Two students with the same grade math will also have the same grade in English.
• D) Two students with the same grade math can have different grades in English.
2. Phatburger features a soda bar, where you can serve your own soft drinks in any size. Do you think that the number of calories in a serving of Zap Kola is a function of the number of fluid ounces?
• Yes
• No
Explain why or why not.
• A) The number of calories is proportional to the number of fluid ounces.
• B) Two servings with the same calories will have different fluid ounces.
• C) Two servings with the same fluid ounces will have different calories.
$$\text{No}$$
$$\text{Choice 2}$$
$$\text{Yes}$$
$$\text{A) The ... fluid ounces.}$$
Solution.
1. No, students with the same grade in English can have different grades in algebra.
2. Yes, the number of calories is proportional to the number of fluid ounces.
A function can be described in several different ways. In the following examples, we consider functions defined by tables, by graphs, and by equations.

### Subsection5.1.2Functions Defined by Tables

When we use a table to describe a function, the first variable in the table (the left column of a vertical table or the top row of a horizontal table) is the input variable, and the second variable is the output. We say that the output variable is a function of the input.

#### Example5.1.5.

1. The table below shows data on sales compiled over several years by the accounting office for Eau Claire Auto Parts, a division of Major Motors. In this example, the year is the input variable, and total sales is the output. We say that total sales, $$S\text{,}$$ is a function of $$t\text{.}$$
 Year $$(t)$$ Total sales $$(S)$$ 2000 $612,000 2001$663,000 2002 $692,000 2003$749,000 2004 $904,000 2. The table below gives the cost of sending a letter by first-class mail in 2022.  Weight in ounces $$(w)$$ Postage $$(P)$$ $$0 \lt w \le 1$$$0.60 $$1 \lt w \le 2$$ $0.84 $$2 \lt w \le 3$$$1.08 $$3 \lt w \le 4$$ $1.32 $$4 \lt w \le 5$$$1.56 $$5 \lt w \le 6$$ $1.80 $$6 \lt w \le 7$$$2.04

#### Checkpoint5.1.7.Practice 2.

Decide whether each table describes $$y$$ as a function of $$x\text{.}$$ Explain your choice.
1.  $$x$$ $$3.5$$ $$2.0$$ $$2.5$$ $$3.5$$ $$2.5$$ $$4.0$$ $$2.5$$ $$3.0$$ $$y$$ $$2.5$$ $$3.0$$ $$2.5$$ $$4.0$$ $$3.5$$ $$4.0$$ $$2.0$$ $$2.5$$
Is $$y$$ a function of $$x\text{?}$$
• Yes
• No
• Each value of $$x$$ has exactly one value of $$y$$ associated with it.
• For example, $$x=3.5$$ corresponds both to $$y=2.5$$ and also to $$y=4.0$$
1.  $$x$$ $$-3$$ $$-2$$ $$-1$$ $$0$$ $$1$$ $$2$$ $$3$$ $$y$$ $$17$$ $$3$$ $$0$$ $$-1$$ $$0$$ $$3$$ $$17$$
Is $$y$$ a function of $$x\text{?}$$
• Yes
• No
• Each value of $$x$$ has exactly one value of $$y$$ associated with it.
• For example, $$y=3$$ corresponds both to $$x=-2$$ and also to $$x=2$$
$$\text{No}$$
$$\text{Choice 2}$$
$$\text{Yes}$$
$$\text{Choice 1}$$
Solution.
1. No, for example, $$x=3.5$$ corresponds both to $$y=2.5$$ and also to $$y=4\text{.}$$
2. Yes, each value of $$x$$ has exactly one value of $$y$$ associated with it.

#### Checkpoint5.1.8.QuickCheck 2.

How would you know if a table of values does not come from a function?
• A) The output values are all the same.
• B) The input values are not evely spaced.
• C) Two different input values have the same output value.
• D) Two different output values have the same input value.
$$\text{D) Two ... input value.}$$
Solution.
Two different output values have the same input value.

### Subsection5.1.3Functions Defined by Graphs

We can also use a graph to define a function. The input variable is displayed on the horizontal axis, and the output variable on the vertical axis.

#### Example5.1.9.

The graph shows the number of hours, $$H\text{,}$$ that the sun is above the horizon in Peoria, Illinois, on day $$t\text{,}$$ where $$t = 0$$ on January 1.
1. Which variable is the input, and which is the output?
2. How many hours of sunlight are there in Peoria on day 150?
3. On which days are there 12 hours of sunlight?
4. What are the maximum and minimum values of $$H\text{,}$$ and when do these values occur? Solution.
1. The input variable, $$t\text{,}$$ appears on the horizontal axis. The number of daylight hours, $$H\text{,}$$ is a function of the date. The output variable appears on the vertical axis.
2. The point on the curve where $$t = 150$$ has $$H \approx 14.1\text{,}$$ so Peoria gets about 14.1 hours of daylight when $$t = 150\text{,}$$ which is at the end of May.
3. $$H = 12$$ at the two points where $$t \approx 85$$ (in late March) and $$t \approx 270$$ (late September).
4. The maximum value of 14.4 hours occurs on the longest day of the year, when $$t \approx 170\text{,}$$ about three weeks into June. The minimum of 9.6 hours occurs on the shortest day, when $$t \approx 355\text{,}$$ about three weeks into December.

#### Checkpoint5.1.10.Practice 3.

The graph shows the elevation in feet, $$a\text{,}$$ of the Los Angeles Marathon course at a distance $$d$$ miles into the race. (Source: Los Angeles Times, March 3, 2005) 1. Which variable is the input, and which is the output?
• The input variable is $$d \text{,}$$ and the output variable is $$a \text{.}$$
• The input variable is $$a \text{,}$$ and the output variable is $$d \text{.}$$
2. What is the elevation at mile 20?
3. At what distances is the elevation 150 feet?
The relevant distances (to the nearest half-mile) separated by commas: miles
4. What are the maximum and minimum values of $$a \text{,}$$ and when do these values occur?
The maximum elevation is $$a=$$ feet which occurs at $$d=$$.
5. The runners pass by the Los Angeles Coliseum at about 4.2 miles into the race. What is the elevation there?
Approximately (within 5) feet
$$\text{Choice 1}$$
$$210$$
$$5, 11, 12, 16, 17.5, 18$$
$$300$$
$$0$$
$$165$$
Solution.
1. The input variable is $$d \text{,}$$ and the output variable is $$a \text{.}$$
2. Approximately 210 feet
3. Approximately where $$d\approx 5 \text{,}$$ $$d\approx 11 \text{,}$$ $$d\approx 12 \text{,}$$ $$d\approx 16 \text{,}$$ $$d\approx 17.5 \text{,}$$ and $$d\approx 18$$
4. The maximum value of 300 feet occurs at the start, when $$d = 0 \text{.}$$ The minimum of 85 feet occurs when $$d\approx 15 \text{.}$$
5. Approximately 165 feet

### Subsection5.1.4Functions Defined by Equations

Example 5.1.11 illustrates a function defined by an equation.

#### Example5.1.11.

As of 2020, One World Trade Center in New York City is the nation’s tallest building, at 1776 feet. If an algebra book is dropped from the top of One World Trade Center, its height above the ground after $$t$$ seconds is given by the equation
\begin{equation*} h = 1776 - 16t^2 \end{equation*}
Thus, after $$\alert{1}$$ second the book’s height is
\begin{equation*} h = 1776 - 16(\alert{1})^2 = 1760 \text{ feet} \end{equation*}
After $$\alert{2}$$ seconds its height is
\begin{equation*} h = 1776 - 16(\alert{2})^2 = 1712 \text{ feet} \end{equation*}
For this function, $$t$$ is the input variable and $$h$$ is the output variable. For any value of $$t\text{,}$$ a unique value of $$h$$ can be determined from the equation for $$h\text{.}$$ We say that $$h$$ is a function of $$t\text{.}$$

#### Checkpoint5.1.12.Practice 4.

Write an equation that gives the volume, $$V\text{,}$$ of a sphere as a function of its radius, $$r\text{.}$$
$$V=$$
$${\frac{4}{3}}\pi r^{3}$$
Solution.
$$V=\dfrac{4}{3}\pi r^3$$

#### Checkpoint5.1.13.QuickCheck 3.

Name three ways to describe a function.
• A) By inputs, outputs, or evaluation
• B) By tables, equations, or graphs
• C) By the intercepts, the slope, or the vertex
• D) By numbers, letters, or diagrams
$$\text{B) By ... , or graphs}$$
Solution.
By tables, equations, or graphs

### Subsection5.1.5Function Notation

There is a convenient notation for discussing functions. First, we choose a letter, such as $$f\text{,}$$ $$g\text{,}$$ or $$h$$ (or $$F\text{,}$$ $$G\text{,}$$ or $$H$$), to name a particular function. (We can use any letter, but these are the most common choices.)
For instance, in Example 5.1.11, the height, $$h\text{,}$$ of a falling algebra book is a function of the elapsed time, $$t\text{.}$$ We might call this function $$f\text{.}$$ In other words, $$f$$ is the name of the relationship between the variables $$h$$ and $$t\text{.}$$ We write
\begin{equation*} h = f (t) \end{equation*}
which means "$$h$$ is a function of $$t\text{,}$$ and $$f$$ is the name of the function."

#### Caution5.1.14.

The new symbol $$f(t)\text{,}$$ read "$$f$$ of $$t\text{,}$$" is another name for the height, $$h\text{.}$$ The parentheses in the symbol $$f(t)$$ do not indicate multiplication. (It would not make sense to multiply the name of a function by a variable.) Think of the symbol $$f(t)$$ as a single variable that represents the output value of the function.
With this new notation we may write
\begin{equation*} h = f (t) = 1776 - 16t^2 \end{equation*}
or just
\begin{equation*} f (t) = 1776 - 16t^2 \end{equation*}
\begin{equation*} h = 1776 - 16t^2 \end{equation*}
to describe the function.

#### Note5.1.15.

Perhaps it seems complicated to introduce a new symbol for $$h\text{,}$$ but the notation $$f(t)$$ is very useful for showing the correspondence between specific values of the variables $$h$$ and $$t\text{.}$$

#### Example5.1.16.

In Example 5.1.11, the height of an algebra book dropped from the top of One World Trade Center is given by the equation
\begin{equation*} h = 1776 - 16t^2 \end{equation*}
We see that
\begin{gather*} \text{when } t=1, \quad h=1760\\ \text{when } t=2, \quad h=1712 \end{gather*}
Using function notation, these relationships can be expressed more concisely as
which we read as "$$f$$ of 1 equals 1760" and "$$f$$ of 2 equals 1712." The values for the input variable, $$t\text{,}$$ appear inside the parentheses, and the values for the output variable, $$h\text{,}$$ appear on the other side of the equation.
Remember that when we write $$y = f(x)\text{,}$$ the symbol $$f(x)$$ is just another name for the output variable.

#### Function Notation. #### Checkpoint5.1.17.QuickCheck 4.

True or False.
1. The notation $$f(t)$$ indicates the product of $$f$$ and $$t\text{.}$$
• True
• False
2. If $$y=f(x)\text{,}$$ then $$f(x)$$ gives the value of the input variable.
• True
• False
3. If $$Q$$ is a function of $$M\text{,}$$ we may write $$M=f(Q)\text{.}$$
• True
• False
4. In the equation $$d=g(n)\text{,}$$ the letters $$d\text{,}$$ $$g\text{,}$$ and $$n$$ are variables.
• True
• False
$$\text{False}$$
$$\text{False}$$
$$\text{False}$$
$$\text{False}$$
Solution.
1. False
2. False
3. False
4. False

#### Checkpoint5.1.18.Practice 5.

Let $$F$$ be the name of the function defined by the graph in Example 5.1.9, the number of hours of daylight in Peoria $$t$$ days after January 1.
1. Use function notation to state that $$H$$ is a function of $$t\text{.}$$
• $$\displaystyle F=H(t)$$
• $$\displaystyle H=F(t)$$
• $$\displaystyle t=F(H)$$
• $$\displaystyle H=t(F)$$
2. What does the statement $$F(15) = 9.7$$ mean in the context of the problem?
• A) The sun is 9.7 degrees above the horizon in Peoria on January 15.
• B) The sun is above the horizon in Peoria for 15 hours on January 10.
• C) The sun is above the horizon in Peoria for 9.7 hours on January 16.
$$\text{Choice 2}$$
$$\text{C) The ... January 16.}$$
Solution.
1. $$\displaystyle H = F(t)$$
2. The sun is above the horizon in Peoria for 9.7 hours on January 16.

#### Checkpoint5.1.19.QuickCheck 5.

Use function notation to write the statement “$$L$$ defines $$w$$ as a function of $$p\text{.}$$
• $$\displaystyle L=w(p)$$
• $$\displaystyle w=L(p)$$
• $$\displaystyle p=L(w)$$
• $$\displaystyle L=p(w)$$
$$\text{Choice 2}$$
Solution.
$$w=L(p)$$

### Subsection5.1.6Using Function Notation

Finding the value of the output variable that corresponds to a particular value of the input variable is called evaluating the function.

#### Example5.1.20.

Let $$g$$ be the name of the postage function defined by the table in Example 5.1.5 b. Find $$g(1)\text{,}$$ $$g(3)\text{,}$$ and $$g(6.75$$).
Solution.
According to the table,
 when $$w=1\text{,}$$ $$p=0.60$$ so $$g(1)=0.60$$ when $$w=3\text{,}$$ $$p=1.00$$ so $$g(3)=1.08$$ when $$w=6.75\text{,}$$ $$p=2.04$$ so $$g(6.75)=2.04$$
Thus, a letter weighing 1 ounce costs $0.60 to mail, a letter weighing 3 ounces costs$1.08, and a letter weighing 6.75 ounces costs $1.04. We can also find the input (or inputs) corresponding to a given output. For example, if $$p=g(w)$$ is the postage function, we solve the equation $$g(w)=0.84$$ by finding all input values, $$w\text{,}$$ that correspond to the output$0.84. According to the table in Example 5.1.5 part (b), any value of $$w$$ greater than 1 but less than or equal to 2 is a solution.

#### Checkpoint5.1.21.Practice 6.

When you exercise, your heart rate should increase until it reaches your target heart rate. The table shows target heart rate, $$r = f(a) \text{,}$$ as a function of age.
 $$a$$ 20 25 30 35 40 45 50 55 60 65 70 $$r$$ 150 146 142 139 135 131 127 124 120 116 112
1. Find $$f(25)$$ and $$f(50) \text{.}$$
$$f(25)=$$
$$f(50)=$$
2. Find a value of $$a$$ for which $$f(a) = 135 \text{.}$$
$$a=$$
$$146$$
$$127$$
$$40$$
Solution.
1. $$f (25) = 146 \text{,}$$ $$f(50) = 127$$
2. $$\displaystyle a = 40$$

#### Checkpoint5.1.22.QuickCheck 6.

If $$n=f(a)\text{,}$$ what are the input and output variables?
• $$f$$ is the output and $$n$$ is the input
• $$a$$ is the input and $$f$$ is the output
• $$a$$ is the input and $$n$$ is the output
• $$f(a)$$ is the input and $$n$$ is the output
$$\text{Choice 3}$$
Solution.
$$a$$ is the input and $$n$$ is the output
To evaluate a function described by an equation, we simply substitute the given input value into the equation to find the corresponding output, or function value.

#### Example5.1.23.

The function $$H$$ is defined by $$~H=f(s) = \dfrac{\sqrt{s+3}}{s}.~~$$ Evaluate the function at the following values.
1. $$\displaystyle s=6$$
2. $$\displaystyle s=-1$$
Solution.
1. $$f(\alert{6})=\dfrac{\sqrt{\alert{6}+3}}{\alert{6}}= \dfrac{\sqrt{9}}{6}=\dfrac{3}{6}=\dfrac{1}{2}\text{.}$$ Thus, $$f(6)=\dfrac{1}{2}\text{.}$$
2. $$f(\alert{-1})=\dfrac{\sqrt{\alert{-1}+3}}{\alert{-1}}= \dfrac{\sqrt{2}}{-1}=-\sqrt{2}\text{.}$$ Thus, $$f(-1)=-\sqrt{2}\text{.}$$

#### Checkpoint5.1.24.Practice 7.

Complete the table displaying ordered pairs for the function $$f(x) = 5 - x^3\text{.}$$ Evaluate the function to find the corresponding $$f(x)$$-value for each value of $$x\text{.}$$
 $$x$$ $$f(x)$$ $$-2$$ $$f(\alert{-2})=5-(\alert{-2})^3=~$$ $$0$$ $$f(\alert{0})=5-\alert{0}^3=$$ $$1$$ $$f(\alert{1})=5-\alert{1}^3=$$ $$3$$ $$f(\alert{3})=5-\alert{3}^3=$$
$$13$$
$$5$$
$$4$$
$$-22$$
Solution.
 $$x$$ $$f(x)$$ $$-2$$ $$13$$ $$0$$ $$5$$ $$1$$ $$4$$ $$3$$ $$-22$$

### Exercises5.1.7Problem Set 5.1

#### Warm Up

##### Exercise Group.
For Problems 1-4, evaluate.
###### 1.
$$2x-x^2~~~$$ for $$x=-4$$
$$-24$$
###### 2.
$$\dfrac{2z-3}{z+2}~~~$$ for $$z=\dfrac{1}{2}$$
###### 3.
$$\sqrt{36-(r+1)^2}~~~$$ for $$r=3$$
$$\sqrt{20}$$
###### 4.
$$-t^3+3t^2~~~$$ for $$t=-2$$
##### Exercise Group.
For Problems 5-8, solve.
###### 5.
$$4-5x-2x^2=1$$
$$-3, \dfrac{1}{2}$$
###### 6.
$$6(2x-8)^2=20$$
###### 7.
$$\dfrac{1}{2x-9}=3$$
$$\dfrac{14}{3}$$
###### 8.
$$5\sqrt{8+x}=20$$

#### Skills Practice

##### 9.
$$x=h(v)=2v^2-3v+1$$
1. Which variable is the input, and which is the output?
2. Evaluate $$h(-2)\text{.}$$
3. Solve $$h(v)=6\text{.}$$
1. input: $$v\text{,}$$ output: $$x$$
2. 15
3. $$-1, \dfrac{5}{2}\text{.}$$
##### 10.
$$A=g(r)=750(1+r)^2$$
1. Which variable is the input, and which is the output?
2. Evaluate $$g(0.04)\text{.}$$
3. Solve $$g(r)=874.80\text{.}$$
##### Exercise Group.
For Problems 11 and 12, evaluate the function.
###### 11.
$$F(x)=\dfrac{1-x}{2x-3}$$
1. $$\displaystyle F(0)$$
2. $$\displaystyle F(-3)$$
3. $$\displaystyle F(\dfrac{5}{2})$$
4. $$\displaystyle F(9.8)$$
1. $$\displaystyle \dfrac{-1}{3}$$
2. $$\displaystyle \dfrac{-4}{9}$$
3. $$\displaystyle \dfrac{-3}{4}$$
4. $$\displaystyle -0.530$$
###### 12.
$$E(t)=\sqrt{t-4}$$
1. $$\displaystyle E(16)$$
2. $$\displaystyle E(4)$$
3. $$\displaystyle E(7)$$
4. $$\displaystyle E(4.2)$$

#### Applications

##### 13.
Which of the following tables define the second variable as a function of the first variable? Explain why or why not.
1.  $$x$$ $$t$$ $$-1$$ $$2$$ $$0$$ $$9$$ $$1$$ $$-2$$ $$0$$ $$-3$$ $$-1$$ $$5$$
2.  $$y$$ $$w$$ $$0$$ $$8$$ $$1$$ $$12$$ $$3$$ $$7$$ $$5$$ $$-3$$ $$7$$ $$4$$
3.  $$x$$ $$y$$ $$-3$$ $$8$$ $$-2$$ $$3$$ $$-1$$ $$0$$ $$0$$ $$-1$$ $$1$$ $$0$$ $$2$$ $$3$$ $$3$$ $$8$$
4.  $$s$$ $$t$$ $$2$$ $$5$$ $$4$$ $$10$$ $$6$$ $$15$$ $$8$$ $$20$$ $$6$$ $$25$$ $$4$$ $$30$$ $$2$$ $$35$$
5.  $$r$$ $$-4$$ $$-2$$ $$0$$ $$2$$ $$4$$ $$v$$ $$6$$ $$6$$ $$3$$ $$6$$ $$8$$
6.  $$p$$ $$-5$$ $$-4$$ $$-3$$ $$-2$$ $$-1$$ $$d$$ $$-5$$ $$-4$$ $$-3$$ $$-2$$ $$-1$$
(b), (c), (e), and (f)
##### 14.
Which of the following tables define the second variable as a function of the first variable? Explain why or why not.
1.  Pressure ($$p$$) Volume ($$v$$) $$15$$ $$100.0$$ $$20$$ $$75.0$$ $$25$$ $$60.0$$ $$30$$ $$50.0$$ $$35$$ $$42.8$$ $$40$$ $$37.5$$ $$45$$ $$33.3$$ $$50$$ $$30.0$$
2.  Frequency ($$f$$) Wavelength ($$w$$) $$5$$ $$60.0$$ $$10$$ $$30.0$$ $$20$$ $$15.0$$ $$30$$ $$10.0$$ $$40$$ $$7.5$$ $$50$$ $$6.0$$ $$60$$ $$5.0$$ $$70$$ $$4.3$$
3.  Temperature ($$T$$) Humidity ($$h$$) Jan. 1 $$\hphantom{000}34\degree$$F $$42\%$$ Jan. 2 $$\hphantom{000}36\degree$$F $$44\%$$ Jan. 3 $$\hphantom{000}35\degree$$F $$47\%$$ Jan. 4 $$\hphantom{000}29\degree$$F $$50\%$$ Jan. 5 $$\hphantom{000}31\degree$$F $$52\%$$ Jan. 6 $$\hphantom{000}35\degree$$F $$51\%$$ Jan. 7 $$\hphantom{000}34\degree$$F $$49\%$$
4.  Inflationrate ($$I$$) Unemploymentrate ($$U$$) 1972 $$\hphantom{000}5.6\%$$ $$5.1\%$$ 1973 $$\hphantom{000}6.2\%$$ $$4.5\%$$ 1974 $$\hphantom{00}10.1\%$$ $$4.9\%$$ 1975 $$\hphantom{000}9.2\%$$ $$7.4\%$$ 1976 $$\hphantom{000}5.8\%$$ $$6.7\%$$ 1977 $$\hphantom{000}5.6\%$$ $$6.8\%$$ 1978 $$\hphantom{000}6.7\%$$ $$7.4\%$$
##### 15.
The function described in Problem 14(a) is called $$g\text{,}$$ so that $$v = g(p)\text{.}$$ Find the following:
1. $$\displaystyle g(25)$$
2. $$\displaystyle g(40)$$
3. $$x$$ so that $$g(x) = 50$$
1. 60
2. 37.5
3. 20
##### 16.
The function described in Problem 14(b) is called $$h\text{,}$$ so that $$w = h(f)\text{.}$$ Find the following:
1. $$\displaystyle h(20)$$
2. $$\displaystyle h(60)$$
3. $$x$$ so that $$h(x) = 10$$
##### Exercise Group.
For Problems 17—24, use the graph of the function to answer the questions.
###### 17.
The graph shows $$C=h(t)\text{,}$$ where $$C$$ stands for the number of customers (in thousands) signed up for a new movie streaming service, measured in months after their advertising campaign at $$t=0$$ in January. 1. When did the service have 2000 customers? Write your answer with function notation.
2. How long did it take that number to double?
3. How long did it take for the number to double again?
4. How many customers signed up between March and April (months 2 and 3)?
1. $$\displaystyle h(1)=2$$
2. 1 month
3. 1 month
4. 4000
###### 18.
The graph shows $$P$$ as a function of $$t\text{.}$$ $$P$$ is the number of houses in Cedar Grove who have had solar panels installed $$t$$ years after 2000. 1. When did 3500 houses have solar panels? Write your answer using function notation.
3. The number of houses with solar panels in Cedar Grove seems to be leveling off at what number?
4. How many houses had solar panels installed between 2001 and 2004?
###### 19.
The graph shows the revenue, $$R=f(d)\text{,}$$ a movie theater collects as a function of the price, $$d\text{,}$$ it charges for a ticket. 1. Estimate the revenue if the theater charges $12.00 for a ticket. 2. What should the theater charge for a ticket in order to collect$1500 in revenue?
3. Write your answers to parts (a) and (b) using function notation.
4. For what values of $$d$$ is $$R \gt 1800\text{?}$$
###### 23.
The bar graph shows the percent of Earth’s surface that lies at various altitudes or depths below the surface of the oceans. (Depths are given as negative altitudes.) (Source: Open University) 1. Read the graph and complete the table.
 Altitude (km) Percent ofEarth’s surface $$-7$$ to $$-6$$  $$-6$$ to $$-5$$  $$-5$$ to $$-4$$  $$-4$$ to $$-3$$  $$-3$$ to $$-2$$  $$-2$$ to $$-1$$  $$-1$$ to $$0$$  $$0$$ to $$1$$  $$1$$ to $$2$$  $$2$$ to $$3$$  $$3$$ to $$4$$  $$4$$ to $$5$$ 
2. What is the most common altitude? What is the second most common altitude?
3. Approximately what percent of the Earth’s surface is below sea level?
4. The height of Mt. Everest is 8.85 kilometers. Can you think of a reason why it is not included in the graph?
###### 24.
Energy is necessary to raise the temperature of a substance, and it is also needed to melt a solid substance to a liquid. The table shows data from heating a solid sample of stearic acid. Heat was applied at a constant rate throughout the experiment.
 Time (minutes) $$0$$ $$0.5$$ $$1.5$$ $$2$$ $$2.5$$ $$3$$ $$4$$ $$5$$ $$6$$ $$7$$ $$8$$ $$8.5$$ $$9$$ $$9.5$$ $$10$$ Temperature ($$\deg C$$) $$19$$ $$29$$ $$40$$ $$48$$ $$53$$ $$55$$ $$55$$ $$55$$ $$55$$ $$55$$ $$55$$ $$64$$ $$70$$ $$73$$ $$74$$
1. Did the temperature rise at a constant rate? Describe the temperature as a function of time.
2. Graph the temperature as a function of time. 3. What is the melting point of stearic acid? How long did it take the sample to melt?
##### 25.
The number of compact cars that a large dealership can sell at price $$p$$ is given by
\begin{equation*} N(p) = \dfrac{12,000,000}{p} \end{equation*}
1. Evaluate $$N(6000)$$ and explain what it means.
2. As $$p$$ increases, does $$N(p)$$ increase or decrease? Support your answer with calculations.
3. Solve the equation $$F(p)=400\text{,}$$ and explain what it means.
1. $$N(6000) = 2000\text{:}$$ 2000 cars will be sold at a price of $6000. 2. decrease 3. 30,000. At a price of$30,000, they will sell 400 cars.
The distance, $$d\text{,}$$ in miles that a person can see on a clear day from a height, $$h\text{,}$$ in feet is given by
1. Evaluate $$G(20,320)$$ and explain what it means.
2. As $$h$$ increases, does $$d$$ increase or decrease? Support your answer with calculations.