# 4.2 Graphs of exponential functions  (Page 5/6)

 Page 5 / 6

Find and graph the equation for a function, $\text{\hspace{0.17em}}g\left(x\right),$ that reflects $\text{\hspace{0.17em}}f\left(x\right)={1.25}^{x}\text{\hspace{0.17em}}$ about the y -axis. State its domain, range, and asymptote.

The domain is $\text{\hspace{0.17em}}\left(-\infty ,\infty \right);\text{\hspace{0.17em}}$ the range is $\text{\hspace{0.17em}}\left(0,\infty \right);\text{\hspace{0.17em}}$ the horizontal asymptote is $\text{\hspace{0.17em}}y=0.$

## Summarizing translations of the exponential function

Now that we have worked with each type of translation for the exponential function, we can summarize them in [link] to arrive at the general equation for translating exponential functions.

Translations of the Parent Function $\text{\hspace{0.17em}}f\left(x\right)={b}^{x}$
Translation Form
Shift
• Horizontally $\text{\hspace{0.17em}}c\text{\hspace{0.17em}}$ units to the left
• Vertically $\text{\hspace{0.17em}}d\text{\hspace{0.17em}}$ units up
$f\left(x\right)={b}^{x+c}+d$
Stretch and Compress
• Stretch if $\text{\hspace{0.17em}}|a|>1$
• Compression if $\text{\hspace{0.17em}}0<|a|<1$
$f\left(x\right)=a{b}^{x}$
Reflect about the x -axis $f\left(x\right)=-{b}^{x}$
Reflect about the y -axis $f\left(x\right)={b}^{-x}={\left(\frac{1}{b}\right)}^{x}$
General equation for all translations $f\left(x\right)=a{b}^{x+c}+d$

## Translations of exponential functions

A translation of an exponential function has the form

Where the parent function, $\text{\hspace{0.17em}}y={b}^{x},$ $\text{\hspace{0.17em}}b>1,$ is

• shifted horizontally $\text{\hspace{0.17em}}c\text{\hspace{0.17em}}$ units to the left.
• stretched vertically by a factor of $\text{\hspace{0.17em}}|a|\text{\hspace{0.17em}}$ if $\text{\hspace{0.17em}}|a|>0.$
• compressed vertically by a factor of $\text{\hspace{0.17em}}|a|\text{\hspace{0.17em}}$ if $\text{\hspace{0.17em}}0<|a|<1.$
• shifted vertically $\text{\hspace{0.17em}}d\text{\hspace{0.17em}}$ units.
• reflected about the x- axis when $\text{\hspace{0.17em}}a<0.$

Note the order of the shifts, transformations, and reflections follow the order of operations.

## Writing a function from a description

Write the equation for the function described below. Give the horizontal asymptote, the domain, and the range.

• $f\left(x\right)={e}^{x}\text{\hspace{0.17em}}$ is vertically stretched by a factor of $\text{\hspace{0.17em}}2\text{\hspace{0.17em}}$ , reflected across the y -axis, and then shifted up $\text{\hspace{0.17em}}4\text{\hspace{0.17em}}$ units.

We want to find an equation of the general form We use the description provided to find $\text{\hspace{0.17em}}a,$ $b,$ $c,$ and $\text{\hspace{0.17em}}d.$

• We are given the parent function $\text{\hspace{0.17em}}f\left(x\right)={e}^{x},$ so $\text{\hspace{0.17em}}b=e.$
• The function is stretched by a factor of $\text{\hspace{0.17em}}2$ , so $\text{\hspace{0.17em}}a=2.$
• The function is reflected about the y -axis. We replace $\text{\hspace{0.17em}}x\text{\hspace{0.17em}}$ with $\text{\hspace{0.17em}}-x\text{\hspace{0.17em}}$ to get: $\text{\hspace{0.17em}}{e}^{-x}.$
• The graph is shifted vertically 4 units, so $\text{\hspace{0.17em}}d=4.$

Substituting in the general form we get,

The domain is $\text{\hspace{0.17em}}\left(-\infty ,\infty \right);\text{\hspace{0.17em}}$ the range is $\text{\hspace{0.17em}}\left(4,\infty \right);\text{\hspace{0.17em}}$ the horizontal asymptote is $\text{\hspace{0.17em}}y=4.$

Write the equation for function described below. Give the horizontal asymptote, the domain, and the range.

• $f\left(x\right)={e}^{x}\text{\hspace{0.17em}}$ is compressed vertically by a factor of $\text{\hspace{0.17em}}\frac{1}{3},$ reflected across the x -axis and then shifted down $\text{\hspace{0.17em}}2$ units.

$f\left(x\right)=-\frac{1}{3}{e}^{x}-2;\text{\hspace{0.17em}}$ the domain is $\text{\hspace{0.17em}}\left(-\infty ,\infty \right);\text{\hspace{0.17em}}$ the range is $\text{\hspace{0.17em}}\left(-\infty ,2\right);\text{\hspace{0.17em}}$ the horizontal asymptote is $\text{\hspace{0.17em}}y=2.$

Access this online resource for additional instruction and practice with graphing exponential functions.

## Key equations

 General Form for the Translation of the Parent Function $f\left(x\right)=a{b}^{x+c}+d$

## Key concepts

• The graph of the function $\text{\hspace{0.17em}}f\left(x\right)={b}^{x}\text{\hspace{0.17em}}$ has a y- intercept at domain range and horizontal asymptote $\text{\hspace{0.17em}}y=0.\text{\hspace{0.17em}}$ See [link] .
• If $\text{\hspace{0.17em}}b>1,$ the function is increasing. The left tail of the graph will approach the asymptote $\text{\hspace{0.17em}}y=0,$ and the right tail will increase without bound.
• If $\text{\hspace{0.17em}}0 the function is decreasing. The left tail of the graph will increase without bound, and the right tail will approach the asymptote $\text{\hspace{0.17em}}y=0.$
• The equation $\text{\hspace{0.17em}}f\left(x\right)={b}^{x}+d\text{\hspace{0.17em}}$ represents a vertical shift of the parent function $\text{\hspace{0.17em}}f\left(x\right)={b}^{x}.$
• The equation $\text{\hspace{0.17em}}f\left(x\right)={b}^{x+c}\text{\hspace{0.17em}}$ represents a horizontal shift of the parent function $\text{\hspace{0.17em}}f\left(x\right)={b}^{x}.\text{\hspace{0.17em}}$ See [link] .
• Approximate solutions of the equation $\text{\hspace{0.17em}}f\left(x\right)={b}^{x+c}+d\text{\hspace{0.17em}}$ can be found using a graphing calculator. See [link] .
• The equation $\text{\hspace{0.17em}}f\left(x\right)=a{b}^{x},$ where $\text{\hspace{0.17em}}a>0,$ represents a vertical stretch if $\text{\hspace{0.17em}}|a|>1\text{\hspace{0.17em}}$ or compression if $\text{\hspace{0.17em}}0<|a|<1\text{\hspace{0.17em}}$ of the parent function $\text{\hspace{0.17em}}f\left(x\right)={b}^{x}.\text{\hspace{0.17em}}$ See [link] .
• When the parent function $\text{\hspace{0.17em}}f\left(x\right)={b}^{x}\text{\hspace{0.17em}}$ is multiplied by $\text{\hspace{0.17em}}-1,$ the result, $\text{\hspace{0.17em}}f\left(x\right)=-{b}^{x},$ is a reflection about the x -axis. When the input is multiplied by $\text{\hspace{0.17em}}-1,$ the result, $\text{\hspace{0.17em}}f\left(x\right)={b}^{-x},$ is a reflection about the y -axis. See [link] .
• All translations of the exponential function can be summarized by the general equation $\text{\hspace{0.17em}}f\left(x\right)=a{b}^{x+c}+d.\text{\hspace{0.17em}}$ See [link] .
• Using the general equation $\text{\hspace{0.17em}}f\left(x\right)=a{b}^{x+c}+d,$ we can write the equation of a function given its description. See [link] .

difference between calculus and pre calculus?
give me an example of a problem so that I can practice answering
x³+y³+z³=42
Robert
dont forget the cube in each variable ;)
Robert
of she solves that, well ... then she has a lot of computational force under her command ....
Walter
what is a function?
I want to learn about the law of exponent
explain this
what is functions?
A mathematical relation such that every input has only one out.
Spiro
yes..it is a relationo of orders pairs of sets one or more input that leads to a exactly one output.
Mubita
Is a rule that assigns to each element X in a set A exactly one element, called F(x), in a set B.
RichieRich
If the plane intersects the cone (either above or below) horizontally, what figure will be created?
can you not take the square root of a negative number
No because a negative times a negative is a positive. No matter what you do you can never multiply the same number by itself and end with a negative
lurverkitten
Actually you can. you get what's called an Imaginary number denoted by i which is represented on the complex plane. The reply above would be correct if we were still confined to the "real" number line.
Liam
Suppose P= {-3,1,3} Q={-3,-2-1} and R= {-2,2,3}.what is the intersection
can I get some pretty basic questions
In what way does set notation relate to function notation
Ama
is precalculus needed to take caculus
It depends on what you already know. Just test yourself with some precalculus questions. If you find them easy, you're good to go.
Spiro
the solution doesn't seem right for this problem
what is the domain of f(x)=x-4/x^2-2x-15 then
x is different from -5&3
Seid
All real x except 5 and - 3
Spiro
***youtu.be/ESxOXfh2Poc
Loree
how to prroved cos⁴x-sin⁴x= cos²x-sin²x are equal
Don't think that you can.
Elliott
By using some imaginary no.
Tanmay
how do you provided cos⁴x-sin⁴x = cos²x-sin²x are equal
What are the question marks for?
Elliott