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1.1
2012 Pearson Education, Inc.
All rights reserved Slide 1.1-1
Limits: A Numerical and
Graphical Approach
OBJECTIVE
•Find limits of functions, if they exist, using
numerical or graphical methods.
2012 Pearson Education, Inc. All rights reserved Slide 1.1-2
Question: As the input x gets “closer” to 3, what happens
to the value of 𝑓(𝑥)?
• Analyze it graphically and numerically
1.1 Limits: A Numerical and Graphical Approach
2
( )3
9xf x
x
2012 Pearson Education, Inc. All rights reserved Slide 1.1-3
Answer: As x gets “closer” to 3, 𝑓(𝑥) gets closer to 6
We write
1.1 Limits: A Numerical and Graphical Approach
3lim ( ) 6x
f x
2012 Pearson Education, Inc. All rights reserved Slide 1.1-4
DEFINITION (informal):
The expression
means “as x gets ‘closer’ to the number a, 𝑓(𝑥) gets closer to the number L”
1.1 Limits: A Numerical and Graphical Approach
lim ( )x a
f x L
2012 Pearson Education, Inc. All rights reserved Slide 1.1-5
Comments
1. x never reaches a
2. The value of 𝑓(𝑎) does not matter (𝑓 𝑎 need not even
be defined)
3. x can approach from either direction, or both directions
1.1 Limits: A Numerical and Graphical Approach
2012 Pearson Education, Inc. All rights reserved Slide 1.1-6
Example: Consider the function 𝐻(𝑥) graphed below
Question: If 𝑥 is less than 1, but gets
closer to 1, what happens to the value
of 𝐻(𝑥)?
Answer: 𝐻(𝑥) gets closer to 4
We write:
Called a limit from the left
1.1 Limits: A Numerical and Graphical Approach
1lim ( ) 4x
H x
2012 Pearson Education, Inc. All rights reserved Slide 1.1-7
Example: Consider the function 𝐻(𝑥) graphed below
Question: If 𝑥 is greater than 1, but gets
closer to 1, what happens to the value
of 𝐻(𝑥)?
Answer: 𝐻(𝑥) gets closer to −2
We write:
Called a limit from the right
1.1 Limits: A Numerical and Graphical Approach
1lim ( ) 1x
H x
1.1 Limits: A Numerical and Graphical Approach
THEOREMS
1. lim𝑥→𝑎
𝑓 𝑥 = 𝐿 if and only if
lim𝑥→𝑎−
𝑓 𝑥 = 𝐿 and lim𝑥→𝑎+
𝑓 𝑥 = 𝐿
2. If lim𝑥→𝑎−
𝑓 𝑥 ≠ lim𝑥→𝑎+
𝑓 𝑥 , then lim𝑥→𝑎
𝑓 𝑥 = 𝐿 does not
exist
2012 Pearson Education, Inc. All rights reserved Slide 1.1-8
2012 Pearson Education, Inc. All rights reserved Slide 1.1-9
Example: Consider the function 𝐻(𝑥) graphed below
Question: Does lim𝑥→1
𝑓 𝑥 exist?
Answer: NO, since the limit
from the left does not equal the
limit from the right
1.1 Limits: A Numerical and Graphical Approach
1 1lim ( ) 4, lim ( ) 1x x
H x H x
2012 Pearson Education, Inc. All rights reserved Slide 1.1-10
Example: Consider the function 𝐻(𝑥) graphed below
Question: Does lim𝑥→−3
𝑓 𝑥 exist?
Answer: Yes, lim𝑥→−3
𝑓 𝑥 = −4
1.1 Limits: A Numerical and Graphical Approach
2012 Pearson Education, Inc. All rights reserved Slide 1.1-11
1.1 Limits: A Numerical and Graphical Approach
Example: Calculate the following limits based on the
graph of 𝑓
a.)
b.)
c.)
2lim ( )x
f x
2lim ( )x
f x
2lim ( )x
f x
= 3
= 3
= 3
Slide 1.1-12
= 0 = 1
= 1 = 1
= 4 = 2
Does not exist = 1
= 1 = 1
2012 Pearson Education, Inc. All rights reserved Slide 1.1-13
Example: Consider the function 𝑓 𝑥 =1
𝑥
Find the following limits:
a) lim𝑥→0−
𝑓 𝑥
b) lim𝑥→0+
𝑓 𝑥
c) lim𝑥→0
𝑓 𝑥
graphically and numerically
1.1 Limits: A Numerical and Graphical Approach
2012 Pearson Education, Inc. All rights reserved Slide 1.1-14
Solutions:
a) lim𝑥→0−
𝑓 𝑥 = −∞
Means: As 𝑥 gets closer to 0 from
the left, 𝑓(𝑥) gets more negative
b) lim𝑥→0+
𝑓 𝑥 = ∞
Means: As 𝑥 gets closer to 0 from
the right, 𝑓(𝑥) gets more positive
c) lim𝑥→0
𝑓 𝑥 Does not exist
1.1 Limits: A Numerical and Graphical Approach
2012 Pearson Education, Inc. All rights reserved Slide 1.1-15
Important Point: ∞ is not a number!
• A number is a destination on the number line
• ∞ is not a destination, it is a journey
1.1 Limits: A Numerical and Graphical Approach
2012 Pearson Education, Inc. All rights reserved Slide 1.1-16
Example: Consider the function 𝑓 𝑥 =1
𝑥
Find the following limits:
a) lim𝑥→−∞
𝑓 𝑥
b) lim𝑥→∞
𝑓 𝑥
graphically and numerically
1.1 Limits: A Numerical and Graphical Approach
2012 Pearson Education, Inc. All rights reserved Slide 1.1-17
Solutions:
a) lim𝑥→−∞
𝑓 𝑥 = 0
Means: As 𝑥 gets more negative,
𝑓(𝑥) gets closer to 0
b) lim𝑥→∞
𝑓 𝑥 = 0
Means: As 𝑥 gets more positive,
𝑓(𝑥) gets closer to 0
1.1 Limits: A Numerical and Graphical Approach
Slide 1.1-18
= 1 = -1
Does not exist = 2
= 0 Does not exist
= 3 = 0
= 1 = 2
2012 Pearson Education, Inc. All rights reserved Slide 1.1-19
2012 Pearson Education, Inc. All rights reserved Slide 1.1-20
= 3.30, 3.30, 3.30
= 2.90, 3.30, Does not exist
2012 Pearson Education, Inc. All rights reserved Slide 1.1-21
Homework
• 1.1 HW
1.1 Limits: A Numerical and Graphical Approach