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Finding Limits: Properties of Limits

For the following exercises, find the limits if lim x c f ( x ) = −3 and lim x c g ( x ) = 5.

lim x c ( f ( x ) + g ( x ) )

2

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lim x c f ( x ) g ( x )

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lim x c ( f ( x ) g ( x ) )

−15

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lim x 0 + f ( x ) , f ( x ) = { 3 x 2 + 2 x + 1 5 x + 3    x > 0 x < 0

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lim x 0 f ( x ) , f ( x ) = { 3 x 2 + 2 x + 1 5 x + 3    x > 0 x < 0

3

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lim x 3 + ( 3 x 〚x〛 )

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For the following exercises, evaluate the limits using algebraic techniques.

lim h 0 ( ( h + 6 ) 2 36 h )

12

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lim x 25 ( x 2 625 x 5 )

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lim x 1 ( x 2 9 x x )

10

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lim x 4 7 12 x + 1 x 4

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lim x 3 ( 1 3 + 1 x 3 + x )

1 9

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Continuity

For the following exercises, use numerical evidence to determine whether the limit exists at x = a . If not, describe the behavior of the graph of the function at x = a .

f ( x ) = 2 x 4 ;   a = 4

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f ( x ) = 2 ( x 4 ) 2 ;   a = 4

At x = 4 , the function has a vertical asymptote.

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f ( x ) = x x 2 x 6 ;   a = 3

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f ( x ) = 6 x 2 + 23 x + 20 4 x 2 25 ;   a = 5 2

removable discontinuity at a = 5 2

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f ( x ) = x 3 9 x ;   a = 9

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For the following exercises, determine where the given function f ( x ) is continuous. Where it is not continuous, state which conditions fail, and classify any discontinuities.

f ( x ) = x 2 2 x 15

continuous on ( , )

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f ( x ) = x 2 2 x 15 x 5

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

removable discontinuity at x = 2. f ( 2 ) is not defined, but limits exist.

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f ( x ) = x 3 125 2 x 2 12 x + 10

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f ( x ) = x 2 1 x 2 x

discontinuity at x = 0 and x = 2. Both f ( 0 ) and f ( 2 ) are not defined.

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f ( x ) = x + 2 x 2 3 x 10

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f ( x ) = x + 2 x 3 + 8

removable discontinuity at x = 2.   f ( 2 ) is not defined.

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Derivatives

For the following exercises, find the average rate of change f ( x + h ) f ( x ) h .

f ( x ) = ln ( x )

ln ( x + h ) ln ( x ) h

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For the following exercises, find the derivative of the function.

Find the equation of the tangent line to the graph of f ( x ) at the indicated x value.
f ( x ) = x 3 + 4 x ; x = 2.

y = 8 x + 16

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For the following exercises, with the aid of a graphing utility, explain why the function is not differentiable everywhere on its domain. Specify the points where the function is not differentiable.

Given that the volume of a right circular cone is V = 1 3 π r 2 h and that a given cone has a fixed height of 9 cm and variable radius length, find the instantaneous rate of change of volume with respect to radius length when the radius is 2 cm. Give an exact answer in terms of π

12 π

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Practice test

For the following exercises, use the graph of f in [link] .

Graph of a piecewise function with two segments. The first segment goes from negative infinity to (-1, 0), an open point, and the second segment goes from (-1, 3), an open point, to positive infinity.

lim x −1 + f ( x )

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lim x −1 f ( x )

0

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lim x −2 f ( x )

−1

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At what values of x is f discontinuous? What property of continuity is violated?

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

f ( x ) = { 1 x 3 ,  i f x 2 x 3 + 1 , i f x > 2    a = 2

lim x 2 f ( x ) = 5 2 a and lim x 2 + f ( x ) = 9 Thus, the limit of the function as x approaches 2 does not exist.

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f ( x ) = { x 3 + 1 , i f x < 1 3 x 2 1 , i f x = 1 x + 3 + 4 , i f x > 1    a = 1

For the following exercises, evaluate each limit using algebraic techniques.

lim x −5 ( 1 5 + 1 x 10 + 2 x )

1 50

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lim h 0 ( h 2 + 25 5 h 2 )

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lim h 0 ( 1 h 1 h 2 + h )

1

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For the following exercises, determine whether or not the given function f is continuous. If it is continuous, show why. If it is not continuous, state which conditions fail.

f ( x ) = x 3 4 x 2 9 x + 36 x 3 3 x 2 + 2 x 6

removable discontinuity at x = 3

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For the following exercises, use the definition of a derivative to find the derivative of the given function at x = a .

f ( x ) = 3 x

f ' ( x ) = 3 2 a 3 2

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For the graph in [link] , determine where the function is continuous/discontinuous and differentiable/not differentiable.

Graph of a piecewise function with three segments. The first segment goes from negative infinity to (-2, -1), an open point; the second segment goes from (-2, -4), an open point, to (0, 0), a closed point; the final segment goes from (0, 1), an open point, to positive infinity.

discontinuous at –2,0, not differentiable at –2,0, 2.

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For the following exercises, with the aid of a graphing utility, explain why the function is not differentiable everywhere on its domain. Specify the points where the function is not differentiable.

f ( x ) = | x 2 | | x + 2 |

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f ( x ) = 2 1 + e 2 x

not differentiable at x = 0 (no limit)

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For the following exercises, explain the notation in words when the height of a projectile in feet, s , is a function of time t in seconds after launch and is given by the function s ( t ) .

s ( 2 )

the height of the projectile at t = 2 seconds

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s ( 2 ) s ( 1 ) 2 1

the average velocity from t = 1  to  t = 2

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For the following exercises, use technology to evaluate the limit.

lim x 0 sin ( x ) 3 x

1 3

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lim x 0 tan 2 ( x ) 2 x

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lim x 0 sin ( x ) ( 1 cos ( x ) ) 2 x 2

0

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Evaluate the limit by hand.

lim x 1 f ( x ) ,  where   f ( x ) = { 4 x 7 x 1 x 2 4 x = 1

At what value(s) of x is the function below discontinuous?

f ( x ) = { 4 x 7 x 1 x 2 4 x = 1

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For the following exercises, consider the function whose graph appears in [link] .

Graph of a positive parabola.

Find the average rate of change of the function from x = 1  to  x = 3.

2

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Find all values of x at which f ' ( x ) = 0.

x = 1

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Find all values of x at which f ' ( x ) does not exist.

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Find an equation of the tangent line to the graph of f the indicated point: f ( x ) = 3 x 2 2 x 6 ,    x = 2

y = 14 x 18

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For the following exercises, use the function f ( x ) = x ( 1 x ) 2 5 .

Graph the function f ( x ) = x ( 1 x ) 2 5 by entering f ( x ) = x ( ( 1 x ) 2 ) 1 5 and then by entering f ( x ) = x ( ( 1 x ) 1 5 ) 2 .

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Explore the behavior of the graph of f ( x ) around x = 1 by graphing the function on the following domains, [0.9, 1.1], [0.99, 1.01], [0.999, 1.001], and [0.9999, 1.0001]. Use this information to determine whether the function appears to be differentiable at x = 1.

The graph is not differentiable at x = 1 (cusp).

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For the following exercises, find the derivative of each of the functions using the definition: lim h 0 f ( x + h ) f ( x ) h

f ( x ) = 4 x 2 7

f ' ( x ) = 8 x

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f ( x ) = 1 x + 2

f ' ( x ) = 1 ( 2 + x ) 2

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f ( x ) = x 3 + 1

f ' ( x ) = 3 x 2

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f ( x ) = x 1

f ' ( x ) = 1 2 x 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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