# 4.8 Fitting exponential models to data  (Page 9/12)

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Use a graphing utility to find an exponential regression formula $\text{\hspace{0.17em}}f\left(x\right)\text{\hspace{0.17em}}$ and a logarithmic regression formula $\text{\hspace{0.17em}}g\left(x\right)\text{\hspace{0.17em}}$ for the points $\text{\hspace{0.17em}}\left(1.5,1.5\right)\text{\hspace{0.17em}}$ and Round all numbers to 6 decimal places. Graph the points and both formulas along with the line $\text{\hspace{0.17em}}y=x\text{\hspace{0.17em}}$ on the same axis. Make a conjecture about the relationship of the regression formulas.

Verify the conjecture made in the previous exercise. Round all numbers to six decimal places when necessary.

First rewrite the exponential with base e : $\text{\hspace{0.17em}}f\left(x\right)=1.034341{e}^{\text{0}\text{.247800x}}.\text{\hspace{0.17em}}$ Then test to verify that $\text{\hspace{0.17em}}f\left(g\left(x\right)\right)=x,$ taking rounding error into consideration:

$\begin{array}{ll}g\left(f\left(x\right)\right)\hfill & =4.035510\mathrm{ln}\left(1.034341{e}^{\text{0}\text{.247800x}}\text{\hspace{0.17em}}\right)-0.136259\hfill \\ \hfill & =4.03551\left(\mathrm{ln}\left(1.034341\right)+\mathrm{ln}\left({e}^{\text{0}\text{.2478}x}\text{\hspace{0.17em}}\right)\right)-0.136259\hfill \\ \hfill & =4.03551\left(\mathrm{ln}\left(1.034341\right)+\text{0}\text{.2478}x\right)-0.136259\hfill \\ \hfill & =0.136257+0.999999x-0.136259\hfill \\ \hfill & =-0.000002+0.999999x\hfill \\ \hfill & \approx 0+x\hfill \\ \hfill & =x\hfill \end{array}$

Find the inverse function $\text{\hspace{0.17em}}{f}^{-1}\left(x\right)\text{\hspace{0.17em}}$ for the logistic function $\text{\hspace{0.17em}}f\left(x\right)=\frac{c}{1+a{e}^{-bx}}.\text{\hspace{0.17em}}$ Show all steps.

Use the result from the previous exercise to graph the logistic model $\text{\hspace{0.17em}}P\left(t\right)=\frac{20}{1+4{e}^{-0.5t}}\text{\hspace{0.17em}}$ along with its inverse on the same axis. What are the intercepts and asymptotes of each function?

The graph of $\text{\hspace{0.17em}}P\left(t\right)\text{\hspace{0.17em}}$ has a y -intercept at (0, 4) and horizontal asymptotes at y = 0 and y = 20. The graph of $\text{\hspace{0.17em}}{P}^{-1}\left(t\right)\text{\hspace{0.17em}}$ has an x - intercept at (4, 0) and vertical asymptotes at x = 0 and x = 20.

## Exponential Functions

Determine whether the function $\text{\hspace{0.17em}}y=156{\left(0.825\right)}^{t}\text{\hspace{0.17em}}$ represents exponential growth, exponential decay, or neither. Explain

exponential decay; The growth factor, $\text{\hspace{0.17em}}0.825,$ is between $\text{\hspace{0.17em}}0\text{\hspace{0.17em}}$ and $\text{\hspace{0.17em}}1.$

The population of a herd of deer is represented by the function $\text{\hspace{0.17em}}A\left(t\right)=205{\left(1.13\right)}^{t},\text{\hspace{0.17em}}$ where $\text{\hspace{0.17em}}t\text{\hspace{0.17em}}$ is given in years. To the nearest whole number, what will the herd population be after $\text{\hspace{0.17em}}6\text{\hspace{0.17em}}$ years?

Find an exponential equation that passes through the points and $\text{\hspace{0.17em}}\left(5,60.75\right).$

$y=0.25{\left(3\right)}^{x}$

Determine whether [link] could represent a function that is linear, exponential, or neither. If it appears to be exponential, find a function that passes through the points.

 x 1 2 3 4 f(x) 3 0.9 0.27 0.081

A retirement account is opened with an initial deposit of $8,500 and earns $\text{\hspace{0.17em}}8.12%\text{\hspace{0.17em}}$ interest compounded monthly. What will the account be worth in $\text{\hspace{0.17em}}20\text{\hspace{0.17em}}$ years? $42,888.18$ Hsu-Mei wants to save$5,000 for a down payment on a car. To the nearest dollar, how much will she need to invest in an account now with $\text{\hspace{0.17em}}7.5%\text{\hspace{0.17em}}$ APR, compounded daily, in order to reach her goal in $\text{\hspace{0.17em}}3\text{\hspace{0.17em}}$ years?

Does the equation $\text{\hspace{0.17em}}y=2.294{e}^{-0.654t}\text{\hspace{0.17em}}$ represent continuous growth, continuous decay, or neither? Explain.

continuous decay; the growth rate is negative.

Suppose an investment account is opened with an initial deposit of $\text{\hspace{0.17em}}\text{10,500}\text{\hspace{0.17em}}$ earning $\text{\hspace{0.17em}}6.25%\text{\hspace{0.17em}}$ interest, compounded continuously. How much will the account be worth after $\text{\hspace{0.17em}}25\text{\hspace{0.17em}}$ years?

## Graphs of Exponential Functions

Graph the function $\text{\hspace{0.17em}}f\left(x\right)=3.5{\left(2\right)}^{x}.\text{\hspace{0.17em}}$ State the domain and range and give the y -intercept.

domain: all real numbers; range: all real numbers strictly greater than zero; y -intercept: (0, 3.5);

Graph the function $\text{\hspace{0.17em}}f\left(x\right)=4{\left(\frac{1}{8}\right)}^{x}\text{\hspace{0.17em}}$ and its reflection about the y -axis on the same axes, and give the y -intercept.

The graph of $\text{\hspace{0.17em}}f\left(x\right)={6.5}^{x}\text{\hspace{0.17em}}$ is reflected about the y -axis and stretched vertically by a factor of $\text{\hspace{0.17em}}7.\text{\hspace{0.17em}}$ What is the equation of the new function, $\text{\hspace{0.17em}}g\left(x\right)?\text{\hspace{0.17em}}$ State its y -intercept, domain, and range.

$g\left(x\right)=7{\left(6.5\right)}^{-x};\text{\hspace{0.17em}}$ y -intercept: Domain: all real numbers; Range: all real numbers greater than $\text{\hspace{0.17em}}0.$

#### Questions & Answers

x=-b+_Гb2-(4ac) ______________ 2a
I've run into this: x = r*cos(angle1 + angle2) Which expands to: x = r(cos(angle1)*cos(angle2) - sin(angle1)*sin(angle2)) The r value confuses me here, because distributing it makes: (r*cos(angle2))(cos(angle1) - (r*sin(angle2))(sin(angle1)) How does this make sense? Why does the r distribute once
so good
abdikarin
this is an identity when 2 adding two angles within a cosine. it's called the cosine sum formula. there is also a different formula when cosine has an angle minus another angle it's called the sum and difference formulas and they are under any list of trig identities
How can you tell what type of parent function a graph is ?
generally by how the graph looks and understanding what the base parent functions look like and perform on a graph
William
if you have a graphed line, you can have an idea by how the directions of the line turns, i.e. negative, positive, zero
William
y=x will obviously be a straight line with a zero slope
William
y=x^2 will have a parabolic line opening to positive infinity on both sides of the y axis vice versa with y=-x^2 you'll have both ends of the parabolic line pointing downward heading to negative infinity on both sides of the y axis
William
y=x will be a straight line, but it will have a slope of one. Remember, if y=1 then x=1, so for every unit you rise you move over positively one unit. To get a straight line with a slope of 0, set y=1 or any integer.
Aaron
yes, correction on my end, I meant slope of 1 instead of slope of 0
William
what is f(x)=
I don't understand
Joe
Typically a function 'f' will take 'x' as input, and produce 'y' as output. As 'f(x)=y'. According to Google, "The range of a function is the complete set of all possible resulting values of the dependent variable (y, usually), after we have substituted the domain."
Thomas
Sorry, I don't know where the "Â"s came from. They shouldn't be there. Just ignore them. :-)
Thomas
Darius
Thanks.
Thomas
Â
Thomas
It is the Â that should not be there. It doesn't seem to show if encloses in quotation marks. "Â" or 'Â' ... Â
Thomas
Now it shows, go figure?
Thomas
what is this?
i do not understand anything
unknown
lol...it gets better
Darius
I've been struggling so much through all of this. my final is in four weeks 😭
Tiffany
this book is an excellent resource! have you guys ever looked at the online tutoring? there's one that is called "That Tutor Guy" and he goes over a lot of the concepts
Darius
thank you I have heard of him. I should check him out.
Tiffany
is there any question in particular?
Joe
I have always struggled with math. I get lost really easy, if you have any advice for that, it would help tremendously.
Tiffany
Sure, are you in high school or college?
Darius
Hi, apologies for the delayed response. I'm in college.
Tiffany
how to solve polynomial using a calculator
So a horizontal compression by factor of 1/2 is the same as a horizontal stretch by a factor of 2, right?
The center is at (3,4) a focus is at (3,-1), and the lenght of the major axis is 26
The center is at (3,4) a focus is at (3,-1) and the lenght of the major axis is 26 what will be the answer?
Rima
I done know
Joe
What kind of answer is that😑?
Rima
I had just woken up when i got this message
Joe
Can you please help me. Tomorrow is the deadline of my assignment then I don't know how to solve that
Rima
i have a question.
Abdul
how do you find the real and complex roots of a polynomial?
Abdul
@abdul with delta maybe which is b(square)-4ac=result then the 1st root -b-radical delta over 2a and the 2nd root -b+radical delta over 2a. I am not sure if this was your question but check it up
Nare
This is the actual question: Find all roots(real and complex) of the polynomial f(x)=6x^3 + x^2 - 4x + 1
Abdul
@Nare please let me know if you can solve it.
Abdul
I have a question
juweeriya
hello guys I'm new here? will you happy with me
mustapha
The average annual population increase of a pack of wolves is 25.
how do you find the period of a sine graph
Period =2π if there is a coefficient (b), just divide the coefficient by 2π to get the new period
Am
if not then how would I find it from a graph
Imani
by looking at the graph, find the distance between two consecutive maximum points (the highest points of the wave). so if the top of one wave is at point A (1,2) and the next top of the wave is at point B (6,2), then the period is 5, the difference of the x-coordinates.
Am
you could also do it with two consecutive minimum points or x-intercepts
Am
I will try that thank u
Imani
Case of Equilateral Hyperbola
ok
Zander
ok
Shella
f(x)=4x+2, find f(3)
Benetta
f(3)=4(3)+2 f(3)=14
lamoussa
14
Vedant
pre calc teacher: "Plug in Plug in...smell's good" f(x)=14
Devante
8x=40
Chris
Explain why log a x is not defined for a < 0
the sum of any two linear polynomial is what
divide simplify each answer 3/2÷5/4
divide simplify each answer 25/3÷5/12
Momo
how can are find the domain and range of a relations
the range is twice of the natural number which is the domain
Morolake