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Real-world applications

For the following exercises, explain the notation in words. The volume f ( t ) of a tank of gasoline, in gallons, t minutes after noon.

f ' ( 30 ) = −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.

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f ' ( 200 ) = 30

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

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For the following exercises, explain the functions in words. The height, s , of a projectile after t seconds is given by s ( t ) = 16 t 2 + 80 t .

s ( 2 ) = 96

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

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s ( 3 ) = 96

The height of the projectile at t = 3 seconds is 96 feet.

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s ( 0 ) = 0 , s ( 5 ) = 0.

The height of the projectile is zero at t = 0 and again at t = 5. In other words, the projectile starts on the ground and falls to earth again after 5 seconds.

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For the following exercises, the volume V of a sphere with respect to its radius r is given by V = 4 3 π r 3 .

Find the average rate of change of V as r changes from 1 cm to 2 cm.

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Find the instantaneous rate of change of V when r = 3  cm .

36 π

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For the following exercises, the revenue generated by selling x items is given by R ( x ) = 2 x 2 + 10 x .

Find the average change of the revenue function as x changes from x = 10 to x = 20.

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Find R ' ( 10 ) and interpret.

$50.00 per unit, which is the instantaneous rate of change of revenue when exactly 10 units are sold.

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Find R ' ( 15 ) and interpret. Compare R ' ( 15 ) to R ' ( 10 ) , and explain the difference.

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For the following exercises, the cost of producing x cellphones is described by the function C ( x ) = x 2 4 x + 1000.

Find the average rate of change in the total cost as x changes from x = 10  to  x = 15.

$21 per unit

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

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

$36

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Extension

For the following exercises, use the definition for the derivative at a point x = a , lim x a f ( x ) f ( a ) x a , to find the derivative of the functions.

f ( x ) = 5 x 2 x + 4

f ' ( x ) = 10 a 1

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f ( x ) = x 2 + 4 x + 7

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f ( x ) = 4 3 x 2

4 ( 3 x ) 2

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Chapter review exercises

Finding Limits: A Numerical and Graphical Approach

For the following exercises, use [link] .

Graph of a piecewise function with two segments. The first segment goes from (-1, 2), a closed point, to (3, -6), a closed point, and the second segment goes from (3, 5), an open point, to (7, 9), a closed point.

lim x −1 + f ( x )

2

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lim x −1 f ( x )

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lim x 1 f ( x )

does not exist

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At what values of x is the function discontinuous? What condition of continuity is violated?

Discontinuous at  x = 1 ( lim x a f ( x )  does not exist ) , x = 3   ( jump discontinuity ) , and  x = 7   ( lim x a f ( x )  does not exist ) .

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Using [link] , estimate lim x 0 f ( x ) .

x F ( x )
−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

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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 x approaches a .   If the function has limit as x approaches a , state it. If not, discuss why there is no limit.

f ( x ) = { | x | 1 , i f x 1 x 3 , i f x = 1    a = 1

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f ( x ) = { 1 x + 1 , i f x = 2 ( x + 1 ) 2 , i f x 2    a = 2

lim x 2 f ( x ) = 1

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f ( x ) = { x + 3 , i f x < 1 x 3 , i f x > 1    a = 1

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Questions & Answers

Ayele, K., 2003. Introductory Economics, 3rd ed., Addis Ababa.
Widad Reply
can you send the book attached ?
Ariel
?
Ariel
What is economics
Widad Reply
the study of how humans make choices under conditions of scarcity
AI-Robot
U(x,y) = (x×y)1/2 find mu of x for y
Desalegn Reply
U(x,y) = (x×y)1/2 find mu of x for y
Desalegn
what is ecnomics
Jan Reply
this is the study of how the society manages it's scarce resources
Belonwu
what is macroeconomic
John Reply
macroeconomic is the branch of economics which studies actions, scale, activities and behaviour of the aggregate economy as a whole.
husaini
etc
husaini
difference between firm and industry
husaini Reply
what's the difference between a firm and an industry
Abdul
firm is the unit which transform inputs to output where as industry contain combination of firms with similar production 😅😅
Abdulraufu
Suppose the demand function that a firm faces shifted from Qd  120 3P to Qd  90  3P and the supply function has shifted from QS  20  2P to QS 10  2P . a) Find the effect of this change on price and quantity. b) Which of the changes in demand and supply is higher?
Toofiq Reply
explain standard reason why economic is a science
innocent Reply
factors influencing supply
Petrus Reply
what is economic.
Milan Reply
scares means__________________ends resources. unlimited
Jan
economics is a science that studies human behaviour as a relationship b/w ends and scares means which have alternative uses
Jan
calculate the profit maximizing for demand and supply
Zarshad Reply
Why qualify 28 supplies
Milan
what are explicit costs
Nomsa Reply
out-of-pocket costs for a firm, for example, payments for wages and salaries, rent, or materials
AI-Robot
concepts of supply in microeconomics
David Reply
economic overview notes
Amahle Reply
identify a demand and a supply curve
Salome Reply
i don't know
Parul
there's a difference
Aryan
Demand curve shows that how supply and others conditions affect on demand of a particular thing and what percent demand increase whith increase of supply of goods
Israr
Hi Sir please how do u calculate Cross elastic demand and income elastic demand?
Abari
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Practice Key Terms 7

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Source:  OpenStax, Precalculus. OpenStax CNX. Jan 19, 2016 Download for free at https://legacy.cnx.org/content/col11667/1.6
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