3.2: Domain and Range (2024)

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Learning Objectives

In this section, you will:

Find the domain of a function defined by an equation.
Graph piecewise-defined functions.

If you’re in the mood for a scary movie, you may want to check out one of the five most popular horror movies of all time—I am Legend, Hannibal, The Ring, The Grudge, and The Conjuring. Figure 1 shows the amount, in dollars, each of those movies grossed when they were released as well as the ticket sales for horror movies in general by year. Notice that we can use the data to create a function of the amount each movie earned or the total ticket sales for all horror movies by year. In creating various functions using the data, we can identify different independent and dependent variables, and we can analyze the data and the functions to determine the domain and range. In this section, we will investigate methods for determining the domain and range of functions such as these.

Figure 1 Based on data compiled by www.the-numbers.com.³

Finding the Domain of a Function Defined by an Equation

In Functions and Function Notation, we were introduced to the concepts of domain and range. In this section, we will practice determining domains and ranges for specific functions. Keep in mind that, in determining domains and ranges, we need to consider what is physically possible or meaningful in real-world examples, such as tickets sales and year in the horror movie example above. We also need to consider what is mathematically permitted. For example, we cannot include any input value that leads us to take an even root of a negative number if the domain and range consist of real numbers. Or in a function expressed as a formula, we cannot include any input value in the domain that would lead us to divide by 0.

We can visualize the domain as a “holding area” that contains “raw materials” for a “function machine” and the range as another “holding area” for the machine’s products. See Figure 2.

Figure 2

We can write the domain and range in interval notation, which uses values within brackets to describe a set of numbers. In interval notation, we use a square bracket [ when the set includes the endpoint and a parenthesis ( to indicate that the endpoint is either not included or the interval is unbounded. For example, if a person has $100 to spend, he or she would need to express the interval that is more than 0 and less than or equal to 100 and write $(0, 100] .$ We will discuss interval notation in greater detail later.

Let’s turn our attention to finding the domain of a function whose equation is provided. Oftentimes, finding the domain of such functions involves remembering three different forms. First, if the function has no denominator or an odd root, consider whether the domain could be all real numbers. Second, if there is a denominator in the function’s equation, exclude values in the domain that force the denominator to be zero. Third, if there is an even root, consider excluding values that would make the radicand negative.

Before we begin, let us review the conventions of interval notation:

The smallest term from the interval is written first.
The largest term in the interval is written second, following a comma.
Parentheses, ( or ), are used to signify that an endpoint is not included, called exclusive.
Brackets, [ or ], are used to indicate that an endpoint is included, called inclusive.

See Figure 3 for a summary of interval notation.

Figure 3

Example 1

Finding the Domain of a Function as a Set of Ordered Pairs

Find the domain of the following function: ${(2, 10), (3, 10), (4, 20), (5, 30), (6, 40)}$ .

Answer

First identify the input values. The input value is the first coordinate in an ordered pair. There are no restrictions, as the ordered pairs are simply listed. The domain is the set of the first coordinates of the ordered pairs.

${2, 3, 4, 5, 6}$

Try It #1

Find the domain of the function:

${(−5, 4), (0, 0), (5, −4), (10, −8), (15, −12)}$

How To

Given a function written in equation form, find the domain.

Identify the input values.
Identify any restrictions on the input and exclude those values from the domain.
Write the domain in interval form, if possible.

Example 2

Finding the Domain of a Function

Find the domain of the function $f (x) = x^{2} - 1.$

Answer

The input value, shown by the variable $x$ in the equation, is squared and then the result is lowered by one. Any real number may be squared and then be lowered by one, so there are no restrictions on the domain of this function. The domain is the set of real numbers.

In interval form, the domain of $f$ is $(- \infty, \infty) .$

Try It #2

Find the domain of the function: $f (x) = 5 - x + x^{3} .$

How To

Given a function written in an equation form that includes a fraction, find the domain.

Identify the input values.
Identify any restrictions on the input. If there is a denominator in the function’s formula, set the denominator equal to zero and solve for $x$ . If the function’s formula contains an even root, set the radicand greater than or equal to 0, and then solve.
Write the domain in interval form, making sure to exclude any restricted values from the domain.

Example 3

Finding the Domain of a Function Involving a Denominator

Find the domain of the function $f (x) = \frac{x + 1}{2 - x} .$

Answer

When there is a denominator, we want to include only values of the input that do not force the denominator to be zero. So, we will set the denominator equal to 0 and solve for $x .$

$\begin{array}{l} 2 - x = 0 \\ - x = - 2 \\ x = 2 \end{array}$

Now, we will exclude 2 from the domain. The answers are all real numbers where $x < 2$ or $x > 2.$ We can use a symbol known as the union, $\cup,$ to combine the two sets. In interval notation, we write the solution: $(−∞, 2) \cup (2, \infty) .$

Figure 4

In interval form, the domain of $f$ is $(- \infty, 2) \cup (2, \infty) .$

Try It #3

Find the domain of the function: $f (x) = \frac{1 + 4 x}{2 x - 1} .$

How To

Given a function written in equation form including an even root, find the domain.

Identify the input values.
Since there is an even root, exclude any real numbers that result in a negative number in the radicand. Set the radicand greater than or equal to zero and solve for $x .$
The solution(s) are the domain of the function. If possible, write the answer in interval form.

Example 4

Finding the Domain of a Function with an Even Root

Find the domain of the function $f (x) = \sqrt{7 - x} .$

Answer

When there is an even root in the formula, we exclude any real numbers that result in a negative number in the radicand.

Set the radicand greater than or equal to zero and solve for $x .$

$\begin{array}{l} 7 - x \geq 0 \\ - x \geq - 7 \\ x \leq 7 \end{array}$

Now, we will exclude any number greater than 7 from the domain. The answers are all real numbers less than or equal to $7,$ or $(- \infty, 7] .$

Try It #4

Find the domain of the function $f (x) = \sqrt{5 + 2 x} .$

Q&A

Can there be functions in which the domain and range do not intersect at all?

Yes. For example, the function $f (x) = - \frac{1}{\sqrt{x}}$ has the set of all positive real numbers as its domain but the set of all negative real numbers as its range. As a more extreme example, a function’s inputs and outputs can be completely different categories (for example, names of weekdays as inputs and numbers as outputs, as on an attendance chart), in such cases the domain and range have no elements in common.

Using Notations to Specify Domain and Range

In the previous examples, we used inequalities and lists to describe the domain of functions. We can also use inequalities, or other statements that might define sets of values or data, to describe the behavior of the variable in set-builder notation. For example, ${x | 10 \leq x < 30}$ describes the behavior of $x$ in set-builder notation. The braces ${}$ are read as “the set of,” and the vertical bar | is read as “such that,” so we would read ${x | 10 \leq x < 30}$ as “the set of x-values such that 10 is less than or equal to $x,$ and $x$ is less than 30.”

Figure 5 compares inequality notation, set-builder notation, and interval notation.

Figure 5

To combine two intervals using inequality notation or set-builder notation, we use the word “or.” As we saw in earlier examples, we use the union symbol, $\cup,$ to combine two unconnected intervals. For example, the union of the sets ${2, 3, 5}$ and ${4, 6}$ is the set ${2, 3, 4, 5, 6} .$ It is the set of all elements that belong to one or the other (or both) of the original two sets. For sets with a finite number of elements like these, the elements do not have to be listed in ascending order of numerical value. If the original two sets have some elements in common, those elements should be listed only once in the union set. For sets of real numbers on intervals, another example of a union is

${x | | x | \geq 3} = (- \infty, - 3] \cup [3, \infty)$

Set-Builder Notation and Interval Notation

Set-builder notation is a method of specifying a set of elements that satisfy a certain condition. It takes the form ${x | statement about x}$ which is read as, “the set of all $x$ such that the statement about $x$ is true.” For example,

${x | 4 < x \leq 12}$

Interval notation is a way of describing sets that include all real numbers between a lower limit that may or may not be included and an upper limit that may or may not be included. The endpoint values are listed between brackets or parentheses. A square bracket indicates inclusion in the set, and a parenthesis indicates exclusion from the set. For example,

$(4, 12]$

How To

Given a line graph, describe the set of values using interval notation.

Identify the intervals to be included in the set by determining where the heavy line overlays the real line.
At the left end of each interval, use [ with each end value to be included in the set (solid dot) or ( for each excluded end value (open dot).
At the right end of each interval, use ] with each end value to be included in the set (filled dot) or ) for each excluded end value (open dot).
Use the union symbol $\cup$ to combine all intervals into one set.

Example 5

Describing Sets on the Real-Number Line

Describe the intervals of values shown in Figure 6 using inequality notation, set-builder notation, and interval notation.

Figure 6

Answer

To describe the values, $x,$ included in the intervals shown, we would say, “ $x$ is a real number greater than or equal to 1 and less than or equal to 3, or a real number greater than 5.”

Inequality	$1 \leq x \leq 3 or x > 5$
Set-builder notation	${x \| 1 \leq x \leq 3 or x > 5}$
Interval notation	$[1, 3] \cup (5, \infty)$

Remember that, when writing or reading interval notation, using a square bracket means the boundary is included in the set. Using a parenthesis means the boundary is not included in the set.

Try It #5

Given Figure 7, specify the graphed set in

ⓐ words
ⓑ set-builder notation
ⓒ interval notation

Figure 7

Finding Domain and Range from Graphs

Another way to identify the domain and range of functions is by using graphs. Because the domain refers to the set of possible input values, the domain of a graph consists of all the input values shown on the x-axis. The range is the set of possible output values, which are shown on the y-axis. Keep in mind that if the graph continues beyond the portion of the graph we can see, the domain and range may be greater than the visible values. See Figure 8.

Figure 8

We can observe that the graph extends horizontally from $−5$ to the right without bound, so the domain is $[−5, \infty) .$ The vertical extent of the graph is all range values $5$ and below, so the range is $(−∞, 5] .$ Note that the domain and range are always written from smaller to larger values, or from left to right for domain, and from the bottom of the graph to the top of the graph for range.

Example 6

Finding Domain and Range from a Graph

Find the domain and range of the function $f$ whose graph is shown in Figure 9.

Figure 9

Answer

We can observe that the horizontal extent of the graph is –3 to 1, so the domain of $f$ is $(- 3, 1] .$

The vertical extent of the graph is 0 to –4, so the range is $[- 4, 0] .$ See Figure 10.

Figure 10

Example 7

Finding Domain and Range from a Graph of Oil Production

Find the domain and range of the function $f$ whose graph is shown in Figure 11.

Figure 11 (credit: modification of work by the U.S. Energy Information Administration)⁴

Answer

The input quantity along the horizontal axis is “years,” which we represent with the variable $t$ for time. The output quantity is “thousands of barrels of oil per day,” which we represent with the variable $b$ for barrels. The graph may continue to the left and right beyond what is viewed, but based on the portion of the graph that is visible, we can determine the domain as $1973 \leq t \leq 2008$ and the range as approximately $180 \leq b \leq 2010.$

In interval notation, the domain is [1973, 2008], and the range is about [180, 2010]. For the domain and the range, we approximate the smallest and largest values since they do not fall exactly on the grid lines.

Try It #6

Given Figure 12, identify the domain and range using interval notation.

Figure 12

Q&A

Can a function’s domain and range be the same?

Yes. For example, the domain and range of the cube root function are both the set of all real numbers.

Finding Domains and Ranges of the Toolkit Functions

We will now return to our set of toolkit functions to determine the domain and range of each.

Figure 13 For the constant function $f (x) = c,$ the domain consists of all real numbers; there are no restrictions on the input. The only output value is the constant $c,$ so the range is the set ${c}$ that contains this single element. In interval notation, this is written as $[c, c],$ the interval that both begins and ends with $c .$

Figure 14 For the identity function $f (x) = x,$ there is no restriction on $x .$ Both the domain and range are the set of all real numbers.

Figure 15 For the absolute value function $f (x) = | x |,$ there is no restriction on $x .$ However, because absolute value is defined as a distance from 0, the output can only be greater than or equal to 0.

Figure 16 For the quadratic function $f (x) = x^{2},$ the domain is all real numbers since the horizontal extent of the graph is the whole real number line. Because the graph does not include any negative values for the range, the range is only nonnegative real numbers.

Figure 17 For the cubic function $f (x) = x^{3},$ the domain is all real numbers because the horizontal extent of the graph is the whole real number line. The same applies to the vertical extent of the graph, so the domain and range include all real numbers.

Figure 18 For the reciprocal function $f (x) = \frac{1}{x},$ we cannot divide by 0, so we must exclude 0 from the domain. Further, 1 divided by any value can never be 0, so the range also will not include 0. In set-builder notation, we could also write ${x | x \neq 0},$ the set of all real numbers that are not zero.

Figure 19 For the reciprocal squared function $f (x) = \frac{1}{x^{2}},$ we cannot divide by $0,$ so we must exclude $0$ from the domain. There is also no $x$ that can give an output of 0, so 0 is excluded from the range as well. Note that the output of this function is always positive due to the square in the denominator, so the range includes only positive numbers.

Figure 20 For the square root function $f (x) = \sqrt[]{x},$ we cannot take the square root of a negative real number, so the domain must be 0 or greater. The range also excludes negative numbers because the square root of a positive number $x$ is defined to be positive, even though the square of the negative number $- \sqrt{x}$ also gives us $x .$

Figure 21 For the cube root function $f (x) = \sqrt[3]{x},$ the domain and range include all real numbers. Note that there is no problem taking a cube root, or any odd-integer root, of a negative number, and the resulting output is negative (it is an odd function).

How To

Given the formula for a function, determine the domain and range.

Exclude from the domain any input values that result in division by zero.
Exclude from the domain any input values that have nonreal (or undefined) number outputs.
Use the valid input values to determine the range of the output values.
Look at the function graph and table values to confirm the actual function behavior.

Example 8

Finding the Domain and Range Using Toolkit Functions

Find the domain and range of $f (x) = 2 x^{3} - x .$

Answer

There are no restrictions on the domain, as any real number may be cubed and then subtracted from the result.

The domain is $(- \infty, \infty)$ and the range is also $(- \infty, \infty) .$

Example 9

Finding the Domain and Range

Find the domain and range of $f (x) = \frac{2}{x + 1} .$

Answer: We cannot evaluate the function at $−1$ because division by zero is undefined. The domain is $(- \infty, −1) \cup (−1, \infty) .$ Because the function is never zero, we exclude 0 from the range. The range is $(- \infty, 0) \cup (0, \infty) .$

Example 10

Finding the Domain and Range

Find the domain and range of $f (x) = 2 \sqrt{x + 4} .$

Answer

We cannot take the square root of a negative number, so the value inside the radical must be nonnegative.

$x + 4 \geq 0 when x \geq - 4$

The domain of $f (x)$ is $[- 4, \infty) .$

We then find the range. We know that $f (- 4) = 0,$ and the function value increases as $x$ increases without any upper limit. We conclude that the range of $f$ is $[0, \infty) .$

Analysis

Figure 22 represents the function $f .$

Figure 22

Try It #7

Find the domain and range of $f (x) = - \sqrt{2 - x} .$

Graphing Piecewise-Defined Functions

Sometimes, we come across a function that requires more than one formula in order to obtain the given output. For example, in the toolkit functions, we introduced the absolute value function $f (x) = | x | .$ With a domain of all real numbers and a range of values greater than or equal to 0, absolute value can be defined as the magnitude, or modulus, of a real number value regardless of sign. It is the distance from 0 on the number line. All of these definitions require the output to be greater than or equal to 0.

If we input 0, or a positive value, the output is the same as the input.

$f (x) = x if x \geq 0$

If we input a negative value, the output is the opposite of the input.

$f (x) = - x if x < 0$

Because this requires two different processes or pieces, the absolute value function is an example of a piecewise function. A piecewise function is a function in which more than one formula is used to define the output over different pieces of the domain.

We use piecewise functions to describe situations in which a rule or relationship changes as the input value crosses certain “boundaries.” For example, we often encounter situations in business for which the cost per piece of a certain item is discounted once the number ordered exceeds a certain value. Tax brackets are another real-world example of piecewise functions. For example, consider a simple tax system in which incomes up to $10,000 are taxed at 10%, and any additional income is taxed at 20%. The tax on a total income $S$ would be $0.1 S$ if $S \leq $ 10, 000$ and $$ 1000 + 0.2 (S - $ 10, 000)$ if $S > $ 10, 000.$

Piecewise Function

A piecewise function is a function in which more than one formula is used to define the output. Each formula has its own domain, and the domain of the function is the union of all these smaller domains. We notate this idea like this:

$f (x) = {\begin{cases} formula 1 if x is in domain 1 \\ formula 2 if x is in domain 2 \\ formula 3 if x is in domain 3 \end{cases}$

In piecewise notation, the absolute value function is

$| x | = {\begin{cases} x if x \geq 0 \\ - x if x < 0 \end{cases}$

How To

Given a piecewise function, write the formula and identify the domain for each interval.

Identify the intervals for which different rules apply.
Determine formulas that describe how to calculate an output from an input in each interval.
Use braces and if-statements to write the function.

Example 11

Writing a Piecewise Function

A museum charges $5 per person for a guided tour with a group of 1 to 9 people or a fixed $50 fee for a group of 10 or more people. Write a function relating the number of people, $n,$ to the cost, $C .$

Answer

Two different formulas will be needed. For n-values under 10, $C = 5 n .$ For values of $n$ that are 10 or greater, $C = 50.$

$C (n) = {\begin{matrix} 5 n & if & 0 < n < 10 \\ 50 & if & n \geq 10 \end{matrix}$

Analysis

The function is represented in Figure 23. The graph is a diagonal line from $n = 0$ to $n = 10$ and a constant after that. In this example, the two formulas agree at the meeting point where $n = 10,$ but not all piecewise functions have this property.

Figure 23

Example 12

Working with a Piecewise Function

A cell phone company uses the function below to determine the cost, $C,$ in dollars for $g$ gigabytes of data transfer.

$C (g) = {\begin{matrix} 25 & if & 0 < g < 2 \\ 25 + 10 (g - 2) & if & g \geq 2 \end{matrix}$

Find the cost of using 1.5 gigabytes of data and the cost of using 4 gigabytes of data.

Answer

To find the cost of using 1.5 gigabytes of data, $C (1.5),$ we first look to see which part of the domain our input falls in. Because 1.5 is less than 2, we use the first formula.

C (1.5) = $ 25

To find the cost of using 4 gigabytes of data, $C (4),$ we see that our input of 4 is greater than 2, so we use the second formula.

$C (4) = 25 + 10 (4 - 2) = $ 45$

Analysis

The function is represented in Figure 24. We can see where the function changes from a constant to a shifted and stretched identity at $g = 2.$ We plot the graphs for the different formulas on a common set of axes, making sure each formula is applied on its proper domain.

How To

Given a piecewise function, sketch a graph.

Indicate on the x-axis the boundaries defined by the intervals on each piece of the domain.
For each piece of the domain, graph on that interval using the corresponding equation pertaining to that piece. Do not graph two functions over one interval because it would violate the criteria of a function.

Example 13

Graphing a Piecewise Function

Sketch a graph of the function.

$f (x) = {\begin{matrix} x^{2} & if & x \leq 1 \\ 3 & if & 1 < x \leq 2 \\ x & if & x > 2 \end{matrix}$

Answer

Each of the component functions is from our library of toolkit functions, so we know their shapes. We can imagine graphing each function and then limiting the graph to the indicated domain. At the endpoints of the domain, we draw open circles to indicate where the endpoint is not included because of a less-than or greater-than inequality; we draw a closed circle where the endpoint is included because of a less-than-or-equal-to or greater-than-or-equal-to inequality.

Figure 25 shows the three components of the piecewise function graphed on separate coordinate systems.

Figure 25 (a) $f (x) = x^{2} if x \leq 1;$ (b) $f (x) = 3 if 1< x \leq 2;$ (c) $f (x) = x if x > 2$

Now that we have sketched each piece individually, we combine them in the same coordinate plane. See Figure 26.

Figure 26

Analysis

Note that the graph does pass the vertical line test even at $x = 1$ and $x = 2$ because the points $(1, 3)$ and $(2, 2)$ are not part of the graph of the function, though $(1, 1)$ and $(2, 3)$ are.

Try It #8

Graph the following piecewise function.

$f (x) = {\begin{matrix} x^{3} & if & x < - 1 \\ - 2 & if & - 1 < x < 4 \\ \sqrt{x} & if & x > 4 \end{matrix}$

Q&A

Can more than one formula from a piecewise function be applied to a value in the domain?

No. Each value corresponds to one equation in a piecewise formula.

Media

Access these online resources for additional instruction and practice with domain and range.

1.2 Section Exercises

Verbal

Why does the domain differ for different functions?

How do we determine the domain of a function defined by an equation?

Explain why the domain of $f (x) = \sqrt[3]{x}$ is different from the domain of $f (x) = \sqrt[]{x} .$

When describing sets of numbers using interval notation, when do you use a parenthesis and when do you use a bracket?

How do you graph a piecewise function?

Algebraic

For the following exercises, find the domain of each function using interval notation.

$f (x) = - 2 x (x - 1) (x - 2)$

$f (x) = 5 - 2 x^{2}$

$f (x) = 3 \sqrt{x - 2}$

$f (x) = 3 - \sqrt{6 - 2 x}$

10.

$f (x) = \sqrt{4 - 3 x}$

11.

$\begin{array}{l} f (x) = \sqrt[]{x^{2} + 4} \end{array}$

12.

$f (x) = \sqrt[3]{1 - 2 x}$

13.

$f (x) = \sqrt[3]{x - 1}$

14.

$f (x) = \frac{9}{x - 6}$

15.

$f (x) = \frac{3 x + 1}{4 x + 2}$

16.

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

17.

$f (x) = \frac{x - 3}{x^{2} + 9 x - 22}$

18.

$f (x) = \frac{1}{x^{2} - x - 6}$

19.

$f (x) = \frac{2 x^{3} - 250}{x^{2} - 2 x - 15}$

20.

$\frac{5}{\sqrt{x - 3}}$

21.

$\frac{2 x + 1}{\sqrt{5 - x}}$

22.

$f (x) = \frac{\sqrt{x - 4}}{\sqrt{x - 6}}$

23.

$f (x) = \frac{\sqrt{x - 6}}{\sqrt{x - 4}}$

24.

$f (x) = \frac{x}{x}$

25.

$f (x) = \frac{x^{2} - 9 x}{x^{2} - 81}$

26.

Find the domain of the function $f (x) = \sqrt{2 x^{3} - 50 x}$ by:

ⓐ using algebra.
ⓑ graphing the function in the radicand and determining intervals on the x-axis for which the radicand is nonnegative.

Graphical

For the following exercises, write the domain and range of each function using interval notation.

27.

28.

29.

30.

31.

32.

33.

34.

35.

36.

37.

For the following exercises, sketch a graph of the piecewise function. Write the domain in interval notation.

38.

$f (x) = {\begin{array}{l} x + 1 & if & x < - 2 \\ - 2 x - 3 & if & x \geq - 2 \end{array}$

39.

$f (x) = {\begin{array}{l} 2 x - 1 & if & x < 1 \\ 1 + x & if & x \geq 1 \end{array}$

40.

$f (x) = {\begin{matrix} x + 1 if x < 0 \\ x - 1 if x > 0 \end{matrix}$

41.

$f (x) = {\begin{matrix} 3 & if & x < 0 \\ \sqrt{x} & if & x \geq 0 \end{matrix}$

42.

$f (x) = {\begin{matrix} x^{2} if x < 0 \\ 1 - x if x > 0 \end{matrix}$

43.

$f (x) = {\begin{array}{r} \begin{array}{r} x^{2} \\ x + 2 \end{array} \end{array} \begin{array}{l} if x < 0 \\ if x \geq 0 \end{array}$

44.

$f (x) = {\begin{matrix} x + 1 & if & x < 1 \\ x^{3} & if & x \geq 1 \end{matrix}$

45.

$f (x) = {\begin{matrix} | x | \\ 1 \end{matrix} \begin{array}{l} if x < 2 \\ if x \geq 2 \end{array}$

Numeric

For the following exercises, given each function $f,$ evaluate $f (−3), f (−2), f (−1),$ and $f (0) .$

46.

$f (x) = {\begin{array}{l} x + 1 & if & x < - 2 \\ - 2 x - 3 & if & x \geq - 2 \end{array}$

47.

$f (x) = {\begin{matrix} 1 & if x \leq - 3 \\ 0 & if x > - 3 \end{matrix}$

48.

$f (x) = {\begin{matrix} - 2 x^{2} + 3 & if x \leq - 1 \\ 5 x - 7 & if x > - 1 \end{matrix}$

For the following exercises, given each function $f,$ evaluate $f (−1), f (0), f (2),$ and $f (4) .$

49.

$f (x) = {\begin{array}{l} 7 x + 3 & if & x < 0 \\ 7 x + 6 & if & x \geq 0 \end{array}$

50.

$f (x) = {\begin{matrix} x^{2} - 2 & if & x < 2 \\ 4 + | x - 5 | & if & x \geq 2 \end{matrix}$

51.

$f (x) = {\begin{matrix} 5 x & if & x < 0 \\ 3 & if & 0 \leq x \leq 3 \\ x^{2} & if & x > 3 \end{matrix}$

For the following exercises, write the domain for the piecewise function in interval notation.

52.

$f (x) = {\begin{matrix} x + 1 if x < - 2 \\ - 2 x - 3 if x \geq - 2 \end{matrix}$

53.

$f (x) = {\begin{matrix} x^{2} - 2 if x < 1 \\ - x^{2} + 2 if x > 1 \end{matrix}$

54.

$f (x) = {\begin{matrix} 2 x - 3 \\ - 3 x^{2} \end{matrix} \begin{matrix} if x < 0 \\ if x \geq 2 \end{matrix}$

Technology

55.

Graph $y = \frac{1}{x^{2}}$ on the viewing window $[−0.5, −0.1]$ and $[0.1, 0.5] .$ Determine the corresponding range for the viewing window. Show the graphs.

56.

Graph $y = \frac{1}{x}$ on the viewing window $[−0.5, −0.1]$ and $[0.1, 0.5] .$ Determine the corresponding range for the viewing window. Show the graphs.

Extension

57.

Suppose the range of a function $f$ is $[−5, 8] .$ What is the range of $| f (x) | ?$

58.

Create a function in which the range is all nonnegative real numbers.

59.

Create a function in which the domain is $x > 2.$

Real-World Applications

60.

The height $h$ of a projectile is a function of the time $t$ it is in the air. The height in feet for $t$ seconds is given by the function $h (t) = −16 t^{2} + 96 t .$ What is the domain of the function? What does the domain mean in the context of the problem?

61.

The cost in dollars of making $x$ items is given by the function $C (x) = 10 x + 500.$

ⓐ The fixed cost is determined when zero items are produced. Find the fixed cost for this item.
ⓑ What is the cost of making 25 items?

Footnotes

3The Numbers: Where Data and the Movie Business Meet. “Box Office History for Horror Movies.” http://www.the-numbers.com/market/genre/Horror. Accessed 3/24/2014
4http://www.eia.gov/dnav/pet/hist/Lea...s=MCRFPAK2&f=A.

FAQs

How do I calculate domain and range? ›

To determine the domain, identify the set of all the x-coordinates on the function's graph. To determine the range, identify the set of all y-coordinates. In addition, ask yourself what are the greatest/least x- and y-values. These values will be your boundary numbers.

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What is the domain and range of 3 variable functions? ›

The domain of a function of three variables is a subset of coordinate 3-space { (x,y,z) | x, y, z ∈ {R} }. The range of a real-valued function f is the collection of all real numbers f(x,y,z) where (x,y,z) is in the domain of f.

What is domain give example? ›

It's the unique name that appears after the @ sign in email addresses, and after www. in web addresses. For instance, the domain name example.com might translate to the physical address 198.102. 434.8. Other examples of domain names are google.com and wikipedia.org.

How find the range of a function? ›

The range of a function is the y-values of the equation or graph. To find the range of the function graphically, inspect the graph from the bottom to the top. If the graph is continuous, the range is all real numbers. If there are holes or breaks in between, then the range does not include those y-values.

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How do you find the domain formula? ›

How To

Identify the input values.
Since there is an even root, exclude any real numbers that result in a negative number in the radicand. Set the radicand greater than or equal to zero and solve for x .
The solution(s) are the domain of the function. If possible, write the answer in interval form.

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How is domain value calculated? ›

The easier option for finding the estimated value of your domain is to use a domain estimation tool. Domain estimation tools enable you to put in your domain name and automatically compare your domain to others like yours. The results of this evaluation are based on what other domains like yours have sold for recently.

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How do you find the domain range and relation? ›

So, if we're given a relation defined as a set of ordered pairs, then we can find the domain of that relation by examining all of the values in the input, or coordinate of each ordered pair, and find the range by taking all of the values in the output, or coordinate of each ordered pair.

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How do you find range if you have function and domain? ›

Overall, the steps for algebraically finding the range of a function are: Write down y=f(x) and then solve the equation for x, giving something of the form x=g(y). Find the domain of g(y), and this will be the range of f(x).

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