# 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 $\text{\hspace{0.17em}}0.$

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
how to prroved cos⁴x-sin⁴x= cos²x-sin²x are equal
Don't think that you can.
Elliott
how do you provided cos⁴x-sin⁴x = cos²x-sin²x are equal
What are the question marks for?
Elliott
Someone should please solve it for me Add 2over ×+3 +y-4 over 5 simplify (×+a)with square root of two -×root 2 all over a multiply 1over ×-y{(×-y)(×+y)} over ×y
For the first question, I got (3y-2)/15 Second one, I got Root 2 Third one, I got 1/(y to the fourth power) I dont if it's right cause I can barely understand the question.
Is under distribute property, inverse function, algebra and addition and multiplication function; so is a combined question
Abena
find the equation of the line if m=3, and b=-2
graph the following linear equation using intercepts method. 2x+y=4
Ashley
how
Wargod
what?
John
ok, one moment
UriEl
how do I post your graph for you?
UriEl
it won't let me send an image?
UriEl
also for the first one... y=mx+b so.... y=3x-2
UriEl
y=mx+b you were already given the 'm' and 'b'. so.. y=3x-2
Tommy
Please were did you get y=mx+b from
Abena
y=mx+b is the formula of a straight line. where m = the slope & b = where the line crosses the y-axis. In this case, being that the "m" and "b", are given, all you have to do is plug them into the formula to complete the equation.
Tommy
thanks Tommy
Nimo
0=3x-2 2=3x x=3/2 then . y=3/2X-2 I think
Given
co ordinates for x x=0,(-2,0) x=1,(1,1) x=2,(2,4)
neil
"7"has an open circle and "10"has a filled in circle who can I have a set builder notation
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
strategies to form the general term
carlmark
consider r(a+b) = ra + rb. The a and b are the trig identity.
Mike
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