Determine whether each example below describes a function.
The area of a circle given its radius.
The number you square to get \(9\text{.}\)
Explanation.
The area of a circle given its radius is a function because there is a set of steps or a formula that changes the radius into the area of the circle. We could write \(A(r)=\pi r^2\text{.}\)
The number you square to get \(9\) is not a function because the process we would apply to get the result does not give a single answer. There are two different answers, \(-3\) and \(3\text{.}\) A function must give a single output for a given input.
Example11.6.2.Tables and Graphs.
Make a table and a graph of the function \(f\text{,}\) where \(f(x)=x^2\text{.}\)
Explanation.
First we will set up a table with negative and positive inputs and calculate the function values. The values are shown in Figure 3, which in turn gives us the graph in Figure 4.
input, \(x\)
output, \(\operatorname{f}(x)\)
\(-3\)
\(9\)
\(-2\)
\(4\)
\(-1\)
\(1\)
\(0\)
\(0\)
\(1\)
\(2\)
\(2\)
\(4\)
\(3\)
\(9\)
Figure11.6.3.
Example11.6.5.Translating between Four Descriptions of the Same Function.
Consider a function \(f\) that triples its input and then adds \(4\text{.}\) Translate this verbal description of \(f\) into a table, a graph, and a formula.
Explanation.
To make a table for \(f\text{,}\) we’ll have to select some input \(x\)-values so we will choose some small negative and positive values that are easy to work with. Given the verbal description, we should be able to compute a column of output values. Table 6 is one possible table that we might end up with.
\(x\)
\(f(x)\)
\(-2\)
\(3(-2)+4=-2\)
\(-1\)
\(3(-1)+4=1\)
\(0 \)
\(3(0)+4=4\)
\(1 \)
\(3(1)+4=7\)
\(2 \)
\(3(2)+4=10\)
Figure11.6.6.
Once we have a table for \(f\text{,}\) we can make a graph for \(f\) as in Figure 7, using the table to plot points.
Lastly, we must find a formula for \(f\text{.}\) This means we need to write an algebraic expression that says the same thing about \(f\) as the verbal description, the table, and the graph. For this example, we can focus on the verbal description. Since \(f\) takes its input, triples it, and adds \(4\text{,}\) we have the formula
In Section 2 we saw the definition of domain and range, and three types of domain restrictions. We also learned how to write the domain and range in interval and set-builder notation.
Example11.6.8.
Determine the domain of \(p\text{,}\) where \(p(x)=\dfrac{x}{2x-1}\text{.}\)
Explanation.
This is an example of the first type of domain restriction, when you have a variable in the denominator. The denominator cannot equal \(0\) so a bad value for \(x\) would be when
The domain is all real numbers except \(\frac{1}{2}\text{.}\)
Example11.6.9.
What is the domain of the function \(C\text{,}\) where \(C(x)=\sqrt{2x-3}-5\text{?}\)
Explanation.
This is an example of the second type of domain restriction where the value inside the radical cannot be negative. So the good values for \(x\) would be when
So on a number line, if we wanted to picture the domain of \(C\text{,}\) we would make a sketch like:
The domain is the interval \(\left[\frac{3}{2},\infty\right)\text{.}\)
Example11.6.10.Range.
Find the range of the function \(q\) using its graph shown in Figure 11.
Explanation.
The range is the collection of possible numbers that \(q\) can give for output. Figure 11 displays a graph of \(q\text{,}\) with the range shown as an interval on the \(y\)-axis.
The output values are the \(y\)-coordinates so we can see that the \(y\)-values start from \(1\) and continue downward forever. Therefore the range is \((-\infty,1]\text{.}\)
Subsection11.6.3Using Technology to Explore Functions
In Section 3 we covered how to find a good graphing window and use it to identify all of the key features of a function. We also learned how to solve equations and inequalities using a graph. Here are some examples for review.
Example11.6.12.Finding an Appropriate Window.
Graph the function \(t\text{,}\) where \(t(x)=(x+10)^2-15\text{,}\) using technology and find a good viewing window.
Explanation.
After some trial and error we found this window that goes from \(-20\) to \(2\) on the \(x\)-axis and \(-20\) to \(100\) on the \(y\)-axis.
Now we can see the vertex and all of the intercepts and we will identify them in the next example.
Example11.6.15.Using Technology to Determine Key Features of a Graph.
Use the previous graph in figure 14 to identify the intercepts, minimum or maximum function value, and the domain and range of the function \(t\text{,}\) where \(t(x)=(x+10)^2-15\text{.}\)
Explanation.
From our graph we can now identify the vertex at \((-10,-15)\text{,}\) the \(y\)-intercept at \((0,85)\text{,}\) and the \(x\)-intercepts at approximately \((-13.9,0)\) and \((-6.13,0)\text{.}\)
Example11.6.17.Solving Equations Graphically Using Technology.
Use graphing technology to solve the equation \(t(x)=40\text{,}\) where \(t(x)=(x+10)^2-15\text{.}\)
Explanation.
To solve the equation \(t(x)=40\text{,}\) we need to graph \(y=t(x)\) and \(y=40\) on the same axes and find the \(x\)-values where they intersect.
From the graph we can see that the intersection points are approximately \((-17.4,40)\) and \((-2.58,40)\text{.}\) The solution set is \(\{-17.4,-2.58\}\text{.}\)
Subsection11.6.4Simplifying Expressions with Function Notation
In Section 4 we learned about the difference between \(f(-x)\) and \(-f(x)\) and how to simplify them. We also learned how to simplify other changes to the input and output like \(f(3x)\) and \(\frac{1}{3}f(x)\text{.}\) Here are some examples.
Example11.6.19.Negative Signs in and out of Function Notation.
Find and simplify a formula for \(f(-x)\) and \(-f(x)\text{,}\) where \(f(x)=-3x^2-7x+1\text{.}\)
Explanation.
To find \(f(-x)\text{,}\) we use an input of \(-x\) in our function \(f\) and simplify to get:
If \(g(x)=2x^2-3x-5\text{,}\) find and simplify a formula for \(g(x-1)\text{.}\)
Explanation.
To find \(g(x-1)\text{,}\) we put in \((x-1)\) for the input. It is important to keep the parentheses because we have exponents and negative signs in the function.
Subsection11.6.5Technical Definition of a Function
In Section 5 we gave a formal definition of a function 11.5.2 and learned to identify what is and is not a function with sets or ordered pairs, tables and graphs. We also used the vertical line test 11.5.20.
Example11.6.21.Formally Defining a Function.
We learned that sets of ordered pairs, tables and graphs can meet the formal definition of a function. Here is an example that shows a function in all three forms. We can verify that each input has at most one output.
\(x\)
\(f(x)\)
\(1\)
\(4\)
\(2\)
\(4\)
\(3\)
\(3\)
\(4\)
\(6\)
\(5\)
\(-2\)
Figure11.6.23.The function \(f\) represented as a table.
Example11.6.25.Identifying What is Not a Function.
Teresa will spend \({\$135}\) to purchase some bowls and some plates. Each plate costs \({\$10}\text{,}\) and each bowl costs \({\$3}\text{.}\) The function \(q(x)={-{\frac{10}{3}}x+45}\) models the number of bowls Teresa will purchase, where \(x\) represents the number of plates to be purchased.
Interpret the meaning of \(q(12)={5}\text{.}\)
\(12\) plates and \(5\) bowls can be purchased.
\($12\) will be used to purchase bowls, and \($5\) will be used to purchase plates.
\($5\) will be used to purchase bowls, and \($12\) will be used to purchase plates.
\(5\) plates and \(12\) bowls can be purchased.
2.
Penelope will spend \({\$90}\) to purchase some bowls and some plates. Each plate costs \({\$2}\text{,}\) and each bowl costs \({\$3}\text{.}\) The function \(q(x)={-{\frac{2}{3}}x+30}\) models the number of bowls Penelope will purchase, where \(x\) represents the number of plates to be purchased.
Interpret the meaning of \(q(21)={16}\text{.}\)
\(16\) plates and \(21\) bowls can be purchased.
\($21\) will be used to purchase bowls, and \($16\) will be used to purchase plates.
\(21\) plates and \(16\) bowls can be purchased.
\($16\) will be used to purchase bowls, and \($21\) will be used to purchase plates.
Exercise Group.
3.
Evaluate the function at the given values.
\(\displaystyle{g(x)={\frac{49}{x-3}}}\) .
\(\displaystyle{g(10)=}\) .
\(\displaystyle{g(3)=}\) .
4.
Evaluate the function at the given values.
\(\displaystyle{h(x)={\frac{5}{x-8}}}\) .
\(\displaystyle{h(3)=}\) .
\(\displaystyle{h(8)=}\) .
5.
Use the graph of \(F\) below to evaluate the given expressions. (Estimates are OK.)
\(F(-8)={}\)
\(F(4)={}\)
6.
Use the graph of \(F\) below to evaluate the given expressions. (Estimates are OK.)
\(F(-5)={}\)
\(F(5)={}\)
7.
Use the table of values for \(G\) below to evaluate the given expressions.
\(x\)
\(-2\)
\(1\)
\(4\)
\(7\)
\(10\)
\(G(x)\)
\(1.2\)
\(7.3\)
\(0.5\)
\(0.8\)
\(2.6\)
\(G({4})={}\)
\(G({7})={}\)
8.
Use the table of values for \(H\) below to evaluate the given expressions.
\(x\)
\(1\)
\(2\)
\(3\)
\(4\)
\(5\)
\(H(x)\)
\(9.9\)
\(7.2\)
\(6.5\)
\(1.9\)
\(7.5\)
\(H({1})={}\)
\(H({5})={}\)
9.
Make a table of values for the function \(g\text{,}\) defined by \(g(x)={5x^{2}}\text{.}\) Based on values in the table, sketch a graph of \(g\text{.}\)
\(x\)
\(g(x)\)
\(g(x)=5x^{2}\)
10.
Make a table of values for the function \(g\text{,}\) defined by \(\displaystyle g(x)={\frac{2^{x}-5}{x^{2}+3}}\text{.}\) Based on values in the table, sketch a graph of \(g\text{.}\)
\(x\)
\(g(x)\)
\(\displaystyle g(x)=\frac{2^{x}-5}{x^{2}+3}\)
11.
The following figure has the graph \(y=d(t)\text{,}\) which models a particle’s distance from the starting line in feet, where \(t\) stands for time in seconds since timing started.
Find \(d(9)\text{.}\)
Interpret the meaning of \(d(9)\text{.}\)
The particle was \(3\) feet away from the starting line \(9\) seconds since timing started.
In the first \(9\) seconds, the particle moved a total of \(3\) feet.
In the first \(3\) seconds, the particle moved a total of \(9\) feet.
The particle was \(9\) feet away from the starting line \(3\) seconds since timing started.
Solve \(d(t)={6}\) for \(t\text{.}\)\(t=\)
Interpret the meaning of part c’s solution(s).
The particle was \(6\) feet from the starting line \(2\) seconds since timing started.
The particle was \(6\) feet from the starting line \(2\) seconds since timing started, and again \(8\) seconds since timing started.
The particle was \(6\) feet from the starting line \(8\) seconds since timing started.
The particle was \(6\) feet from the starting line \(2\) seconds since timing started, or \(8\) seconds since timing started.
12.
The following figure has the graph \(y=d(t)\text{,}\) which models a particle’s distance from the starting line in feet, where \(t\) stands for time in seconds since timing started.
Find \(d(7)\text{.}\)
Interpret the meaning of \(d(7)\text{.}\)
In the first \(7\) seconds, the particle moved a total of \(6\) feet.
The particle was \(7\) feet away from the starting line \(6\) seconds since timing started.
The particle was \(6\) feet away from the starting line \(7\) seconds since timing started.
In the first \(6\) seconds, the particle moved a total of \(7\) feet.
Solve \(d(t)={2}\) for \(t\text{.}\)\(t=\)
Interpret the meaning of part c’s solution(s).
The particle was \(2\) feet from the starting line \(1\) seconds since timing started, and again \(9\) seconds since timing started.
The particle was \(2\) feet from the starting line \(9\) seconds since timing started.
The particle was \(2\) feet from the starting line \(1\) seconds since timing started, or \(9\) seconds since timing started.
The particle was \(2\) feet from the starting line \(1\) seconds since timing started.
Domain and Range.
Find the domain and range of each function using its graph.
13.
A function is graphed.
This function has domain and range .
14.
A function is graphed.
This function has domain and range .
15.
A function is graphed.
The function has domain and range .
16.
A function is graphed.
The function has domain and range .
17.
A function is graphed.
The function has domain and range .
18.
A function is graphed.
The function has domain and range .
Exercise Group.
19.
Find the domain of \(A\) where \(\displaystyle{A(x)= \frac{\sqrt{20 + x}}{3 - x}}\text{.}\)
20.
Find the domain of \(p\) where \(\displaystyle{p(x)= \frac{\sqrt{3 + x}}{10 - x}}\text{.}\)
21.
An object was shot up into the air at an initial vertical speed of \(384\) feet per second. Its height as time passes can be modeled by the quadratic function \(f\text{,}\) where \(f(t)={-16t^{2}+384t}\text{.}\) Here \(t\) represents the number of seconds since the object’s release, and \(f(t)\) represents the object’s height in feet.
Find the function’s domain and range in this context.
The function’s domain in this context is .
The function’s range in this context is .
22.
An object was shot up into the air at an initial vertical speed of \(416\) feet per second. Its height as time passes can be modeled by the quadratic function \(f\text{,}\) where \(f(t)={-16t^{2}+416t}\text{.}\) Here \(t\) represents the number of seconds since the object’s release, and \(f(t)\) represents the object’s height in feet.
Find the function’s domain and range in this context.
The function’s domain in this context is .
The function’s range in this context is .
Using Technology to Explore Functions.
23.
Use technology to make a table of values for the function.
\(F(x)={3x^{2}-13x+4}\)
\(x\)
\(F(x)\)
24.
Use technology to make a table of values for the function.
\(F(x)={0.15x^{2}+40x+11}\)
\(x\)
\(F(x)\)
25.
Let \(f(x)={-6970x-1116}\text{.}\) Choose an appropriate window for graphing \(f\) that shows its key features.
The \(x\)-interval could be and the \(y\)-interval could be .
26.
Let \(f(x)={776x-435}\text{.}\) Choose an appropriate window for graphing \(f\) that shows its key features.
The \(x\)-interval could be and the \(y\)-interval could be .
27.
Use technology to make some graphs and determine how many times the graphs of the following curves cross each other.
\(y={\left(347+16x\right)\mathopen{}\left(223-x\right)}\) and \(y={1000}\) intersect
?
zero times
one time
two times
three times
.
28.
Use technology to make some graphs and determine how many times the graphs of the following curves cross each other.
\(y={9x^{3}-3x^{2}-4x}\) and \(y={-x+3}\) intersect
use technology to determine the following. Round answers as necessary.
Any intercepts.
The vertex.
The domain.
The range.
31.
Let \(f(x)=4x^2+5x-1\) and \(g(x)=5\text{.}\) Use graphing technology to determine the following.
What are the points of intersection for these two functions?
Solve \(f(x)=g(x)\text{.}\)
Solve \(f(x)\lt g(x)\text{.}\)
Solve \(f(x)\geq g(x)\text{.}\)
32.
Let \(p(x)=6x^2-3x+4\) and \(k(x)=7\text{.}\) Use graphing technology to determine the following.
What are the points of intersection for these two functions?
Solve \(p(x)=k(x)\text{.}\)
Solve \(p(x)\lt k(x)\text{.}\)
Solve \(p(x)\geq k(x)\text{.}\)
33.
Use graphing technology to solve the equation \(-0.02 x^2 + 1.97 x - 51.5=0.05\left(x-50\right)^2-0.03\left(x-50\right)\text{.}\) Approximate the solution(s) if necessary.
34.
Use graphing technology to solve the equation \(-200x^2+60x-55=-20x-40\text{.}\) Approximate the solution(s) if necessary.
35.
Use graphing technology to solve the inequality \(-15x^2-6\leq 10x-4\text{.}\) State the solution set using interval notation, and approximate if necessary.
36.
Use graphing technology to solve the inequality \(\frac{1}{2}x^2+\frac{3}{2}x \geq \frac{1}{2}x-\frac{3}{2}\text{.}\) State the solution set using interval notation, and approximate if necessary.
Simplifying Expressions with Function Notation.
37.
Let \(f\) be a function given by \(f(x)={-5x^{2}-5x}\text{.}\) Find and simplify the following:
\(f(x) - 2={}\)
\(f(x - 2)={}\)
\(-2f(x)={}\)
\(f(-2x)={}\)
38.
Let \(f\) be a function given by \(f(x)={2x^{2}-x}\text{.}\) Find and simplify the following:
\(f(x) - 3={}\)
\(f(x - 3)={}\)
\(-3f(x)={}\)
\(f(-3x)={}\)
39.
Simplify \(h({-x})\text{,}\) where \(h(x)={-2+6x}\text{.}\)
40.
Simplify \(K(y)+3\text{,}\) where \(K(y)={-3-6.1y}\text{.}\)
41.
Simplify \(7G(y)\text{,}\) where \(G(y)={6y^{2}-3y-7}\text{.}\)
42.
Simplify \(g({-r})\text{,}\) where \(g(r)={-7r^{2}+r-3}\text{.}\)
Technical Definition of a Function.
43.
Does the following set of ordered pairs make for a function of \(x\text{?}\)
\(\Big\{(4,10),(2,1),(-5,8),(3,8),(6,9)\Big\}\)
This set of ordered pairs
?
describes
does not describe
a function of \(x\text{.}\) This set of ordered pairs has domain and range .
44.
Does the following set of ordered pairs make for a function of \(x\text{?}\)
\(\Big\{(3,5),(-1,10),(5,2),(5,0),(-9,7)\Big\}\)
This set of ordered pairs
?
describes
does not describe
a function of \(x\text{.}\) This set of ordered pairs has domain and range .
45.
Below is all of the information that exists about a function \(K\text{.}\)
The following graphs show two relationships. Decide whether each graph shows a relationship where \(y\) is a function of \(x\text{.}\)
The first graph
?
does
does not
give a function of \(x\text{.}\) The second graph
?
does
does not
give a function of \(x\text{.}\)
48.
The following graphs show two relationships. Decide whether each graph shows a relationship where \(y\) is a function of \(x\text{.}\)
The first graph
?
does
does not
give a function of \(x\text{.}\) The second graph
?
does
does not
give a function of \(x\text{.}\)
49.
Some equations involving \(x\) and \(y\) define \(y\) as a function of \(x\text{,}\) and others do not. For example, if \(x+y=1\text{,}\) we can solve for \(y\) and obtain \(y = 1-x\text{.}\) And we can then think of \(y = f(x) =
1-x\text{.}\) On the other hand, if we have the equation \(x=y^2\) then \(y\) is not a function of \(x\text{,}\) since for a given positive value of \(x\text{,}\) the value of \(y\) could equal \(\sqrt{x}\) or it could equal \(-\sqrt{x}\text{.}\) Select all of the following relations that make \(y\) a function of \(x\text{.}\) There are several correct answers.
\(\displaystyle x+y=1\)
\(\displaystyle y^2 + x^2 = 1\)
\(\displaystyle \left|y\right| - x = 0\)
\(\displaystyle 4 x + 8 y + 2 = 0\)
\(\displaystyle y + x^2 = 1\)
\(\displaystyle y^3 + x^4 = 1\)
\(\displaystyle y^6 + x = 1\)
\(\displaystyle y - \left|x\right| = 0\)
On the other hand, some equations involving \(x\) and \(y\) define \(x\) as a function of \(y\) (the other way round).
Select all of the following relations that make \(x\) a function of \(y\text{.}\) There are several correct answers.
\(\displaystyle y^4 + x^5 = 1\)
\(\displaystyle \left|y\right| - x = 0\)
\(\displaystyle y^2 + x^2 = 1\)
\(\displaystyle 4 x + 8 y + 2 = 0\)
\(\displaystyle y - \left|x\right| = 0\)
50.
Some equations involving \(x\) and \(y\) define \(y\) as a function of \(x\text{,}\) and others do not. For example, if \(x+y=1\text{,}\) we can solve for \(y\) and obtain \(y = 1-x\text{.}\) And we can then think of \(y = f(x) =
1-x\text{.}\) On the other hand, if we have the equation \(x=y^2\) then \(y\) is not a function of \(x\text{,}\) since for a given positive value of \(x\text{,}\) the value of \(y\) could equal \(\sqrt{x}\) or it could equal \(-\sqrt{x}\text{.}\) Select all of the following relations that make \(y\) a function of \(x\text{.}\) There are several correct answers.
\(\displaystyle y^3 + x^4 = 1\)
\(\displaystyle y^2 + x^2 = 1\)
\(\displaystyle 6 x + 5 y + 5 = 0\)
\(\displaystyle y + x^2 = 1\)
\(\displaystyle y^6 + x = 1\)
\(\displaystyle y - \left|x\right| = 0\)
\(\displaystyle \left|y\right| - x = 0\)
\(\displaystyle x+y=1\)
On the other hand, some equations involving \(x\) and \(y\) define \(x\) as a function of \(y\) (the other way round).
Select all of the following relations that make \(x\) a function of \(y\text{.}\) There are several correct answers.
\(\displaystyle \left|y\right| - x = 0\)
\(\displaystyle 6 x + 5 y + 5 = 0\)
\(\displaystyle y - \left|x\right| = 0\)
\(\displaystyle y^2 + x^2 = 1\)
\(\displaystyle y^4 + x^5 = 1\)
Exercise Group.
51.
Determine whether or not the following table could be the table of values of a function. If the table can not be the table of values of a function, give an input that has more than one possible output.
Input
Output
\(2\)
\(2\)
\(4\)
\(-15\)
\(6\)
\(14\)
\(8\)
\(-18\)
\(-2\)
\(-12\)
Could this be the table of values for a function?
yes
no
If not, which input has more than one possible output?
-2
2
4
6
8
None, the table represents a function.
52.
Determine whether or not the following table could be the table of values of a function. If the table can not be the table of values of a function, give an input that has more than one possible output.
Input
Output
\(2\)
\(6\)
\(4\)
\(12\)
\(6\)
\(-9\)
\(8\)
\(12\)
\(-2\)
\(-13\)
Could this be the table of values for a function?
yes
no
If not, which input has more than one possible output?
-2
2
4
6
8
None, the table represents a function.
53.
Determine whether or not the following table could be the table of values of a function. If the table can not be the table of values of a function, give an input that has more than one possible output.
Input
Output
\(-4\)
\(-17\)
\(-3\)
\(-4\)
\(-2\)
\(-18\)
\(-3\)
\(26\)
\(-1\)
\(-9\)
Could this be the table of values for a function?
yes
no
If not, which input has more than one possible output?
-4
-3
-2
-1
None, the table represents a function.
54.
Determine whether or not the following table could be the table of values of a function. If the table can not be the table of values of a function, give an input that has more than one possible output.
Input
Output
\(-4\)
\(3\)
\(-3\)
\(-2\)
\(-2\)
\(-1\)
\(-3\)
\(12\)
\(-1\)
\(9\)
Could this be the table of values for a function?
yes
no
If not, which input has more than one possible output?