# 12.4 Derivatives  (Page 10/18)

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## Real-world applications

For the following exercises, explain the notation in words. The volume $\text{\hspace{0.17em}}f\left(t\right)\text{\hspace{0.17em}}$ of a tank of gasoline, in gallons, $\text{\hspace{0.17em}}t\text{\hspace{0.17em}}$ minutes after noon.

$f\left(0\right)=600$

$f\text{'}\left(30\right)=-20$

At 12:30 p.m. , the rate of change of the number of gallons in the tank is –20 gallons per minute. That is, the tank is losing 20 gallons per minute.

$f\left(30\right)=0$

$f\text{'}\left(200\right)=30$

At 200 minutes after noon, the volume of gallons in the tank is changing at the rate of 30 gallons per minute.

$f\left(240\right)=500$

For the following exercises, explain the functions in words. The height, $\text{\hspace{0.17em}}s,$ of a projectile after $\text{\hspace{0.17em}}t\text{\hspace{0.17em}}$ seconds is given by $\text{\hspace{0.17em}}s\left(t\right)=-16{t}^{2}+80t.$

$s\left(2\right)=96$

The height of the projectile after 2 seconds is 96 feet.

$s\text{'}\left(2\right)=16$

$s\left(3\right)=96$

The height of the projectile at $\text{\hspace{0.17em}}t=3\text{\hspace{0.17em}}$ seconds is 96 feet.

$s\text{'}\left(3\right)=-16$

$s\left(0\right)=0,s\left(5\right)=0.$

The height of the projectile is zero at $\text{\hspace{0.17em}}t=0\text{\hspace{0.17em}}$ and again at $\text{\hspace{0.17em}}t=5.\text{\hspace{0.17em}}$ In other words, the projectile starts on the ground and falls to earth again after 5 seconds.

For the following exercises, the volume $\text{\hspace{0.17em}}V\text{\hspace{0.17em}}$ of a sphere with respect to its radius $\text{\hspace{0.17em}}r\text{\hspace{0.17em}}$ is given by $\text{\hspace{0.17em}}V=\frac{4}{3}\pi {r}^{3}.$

Find the average rate of change of $\text{\hspace{0.17em}}V\text{\hspace{0.17em}}$ as $\text{\hspace{0.17em}}r\text{\hspace{0.17em}}$ changes from 1 cm to 2 cm.

Find the instantaneous rate of change of $\text{\hspace{0.17em}}V\text{\hspace{0.17em}}$ when

$36\pi$

For the following exercises, the revenue generated by selling $\text{\hspace{0.17em}}x\text{\hspace{0.17em}}$ items is given by $\text{\hspace{0.17em}}R\left(x\right)=2{x}^{2}+10x.$

Find the average change of the revenue function as $\text{\hspace{0.17em}}x\text{\hspace{0.17em}}$ changes from $\text{\hspace{0.17em}}x=10\text{\hspace{0.17em}}$ to $\text{\hspace{0.17em}}x=20.$

Find $\text{\hspace{0.17em}}R\text{'}\left(10\right)\text{\hspace{0.17em}}$ and interpret.

$50.00 per unit, which is the instantaneous rate of change of revenue when exactly 10 units are sold. Find $\text{\hspace{0.17em}}R\text{'}\left(15\right)\text{\hspace{0.17em}}$ and interpret. Compare $\text{\hspace{0.17em}}R\text{'}\left(15\right)\text{\hspace{0.17em}}$ to $\text{\hspace{0.17em}}R\text{'}\left(10\right),$ and explain the difference. For the following exercises, the cost of producing $\text{\hspace{0.17em}}x\text{\hspace{0.17em}}$ cellphones is described by the function $\text{\hspace{0.17em}}C\left(x\right)={x}^{2}-4x+1000.$ Find the average rate of change in the total cost as $\text{\hspace{0.17em}}x\text{\hspace{0.17em}}$ changes from$21 per unit

Find the approximate marginal cost, when 15 cellphones have been produced, of producing the 16 th cellphone.

Find the approximate marginal cost, when 20 cellphones have been produced, of producing the 21 st cellphone.

\$36

## Extension

For the following exercises, use the definition for the derivative at a point $\text{\hspace{0.17em}}x=a,$ $\text{\hspace{0.17em}}\underset{x\to a}{\mathrm{lim}}\frac{f\left(x\right)-f\left(a\right)}{x-a},$ to find the derivative of the functions.

$f\left(x\right)=\frac{1}{{x}^{2}}$

$f\left(x\right)=5{x}^{2}-x+4$

$f\text{'}\left(x\right)=10a-1$

$f\left(x\right)=-{x}^{2}+4x+7$

$f\left(x\right)=\frac{-4}{3-{x}^{2}}$

$\frac{4}{{\left(3-x\right)}^{2}}$

## Finding Limits: A Numerical and Graphical Approach

For the following exercises, use [link] .

$\underset{x\to {-1}^{+}}{\mathrm{lim}}f\left(x\right)$

2

$\underset{x\to {-1}^{-}}{\mathrm{lim}}f\left(x\right)$

$\underset{x\to -1}{\mathrm{lim}}f\left(x\right)$

does not exist

$\underset{x\to 3}{\mathrm{lim}}f\left(x\right)$

At what values of $\text{\hspace{0.17em}}x$ is the function discontinuous? What condition of continuity is violated?

Using [link] , estimate $\text{\hspace{0.17em}}\underset{x\to 0}{\mathrm{lim}}f\left(x\right).$

 $x$ $F\left(x\right)$ −0.1 2.875 −0.01 2.92 −0.001 2.998 0 Undefined 0.001 2.9987 0.01 2.865 0.1 2.78145 0.15 2.678

3

For the following exercises, with the use of a graphing utility, use numerical or graphical evidence to determine the left- and right-hand limits of the function given as $\text{\hspace{0.17em}}x\text{\hspace{0.17em}}$ approaches If the function has limit as $\text{\hspace{0.17em}}x\text{\hspace{0.17em}}$ approaches $\text{\hspace{0.17em}}a,\text{\hspace{0.17em}}$ state it. If not, discuss why there is no limit.

$\begin{array}{ll}\underset{x\to -2}{\mathrm{lim}}\hfill & f\left(x\right)=1\hfill \end{array}$

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
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
Where do the rays point?
Spiro
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 By By By Abby Sharp By OpenStax By Stephen Voron By John Gabrieli By OpenStax By Brooke Delaney By Jemekia Weeden By John Gabrieli By Karen Gowdey By Mldelatte