Page 1
Limits at Infinity and Asymptotes
Institute of Lifelong Learning, University of Delhi
Lesson: Limits at Infinity and Asymptotes
Course Developer: Brijendra Yadav
Department/College: Assistant Professor, Department of
Mathematics, A.N.D. College, University of Delhi
Page 2
Limits at Infinity and Asymptotes
Institute of Lifelong Learning, University of Delhi
Lesson: Limits at Infinity and Asymptotes
Course Developer: Brijendra Yadav
Department/College: Assistant Professor, Department of
Mathematics, A.N.D. College, University of Delhi
Limits at Infinity and Asymptotes
Institute of Lifelong Learning, University of Delhi
Table of Contents
Chapter: Limits at Infinity and Asymptotes
• 1: Learning Outcomes
• 2: Introduction
• 3: Limits at Infinity
• 4: Infinite Limits at Infinity
• 5: Limits of Rational Functions at Infinity
• 6: Asymptotes
o 6.1. Horizontal Asymptotes
o 6.2. Vertical Asymptotes
o 6.3. Oblique Asymptotes
o 6.4. Dominant Term of a Function
• Exercises
• Summary
• Reference
1. Learning outcomes:
After studying this chapter you should be able to understand the
? Limits at Infinity
? Infinite Limits at Infinity
? Limits of Rational Functions at Infinity
? Asymptotes
? Horizontal Asymptotes
? Vertical Asymptotes
? Oblique Asymptotes
? Dominant Term of a Function
Page 3
Limits at Infinity and Asymptotes
Institute of Lifelong Learning, University of Delhi
Lesson: Limits at Infinity and Asymptotes
Course Developer: Brijendra Yadav
Department/College: Assistant Professor, Department of
Mathematics, A.N.D. College, University of Delhi
Limits at Infinity and Asymptotes
Institute of Lifelong Learning, University of Delhi
Table of Contents
Chapter: Limits at Infinity and Asymptotes
• 1: Learning Outcomes
• 2: Introduction
• 3: Limits at Infinity
• 4: Infinite Limits at Infinity
• 5: Limits of Rational Functions at Infinity
• 6: Asymptotes
o 6.1. Horizontal Asymptotes
o 6.2. Vertical Asymptotes
o 6.3. Oblique Asymptotes
o 6.4. Dominant Term of a Function
• Exercises
• Summary
• Reference
1. Learning outcomes:
After studying this chapter you should be able to understand the
? Limits at Infinity
? Infinite Limits at Infinity
? Limits of Rational Functions at Infinity
? Asymptotes
? Horizontal Asymptotes
? Vertical Asymptotes
? Oblique Asymptotes
? Dominant Term of a Function
Limits at Infinity and Asymptotes
Institute of Lifelong Learning, University of Delhi
2. Introduction:
Asymptotes convey the information about the behavior of curves
and determining the asymptotes of a function is an important step in
sketching its graph. In this lesson, we will study about the limits at
infinity and how to use the concept of limits to find the asymptote of a
function.
3: Limits at Infinity:
Let X be any non-empty subset of R, Let : X R f ? . Suppose that
00
(, ) X x for some x R 8? ? . The function f(x) is said to have a limit R ? ? as
x ? 8 if given any 0 e > there exists
0
() x d de = > such that for any x d > ,
then
() fx e -< ?
Limit at infinity is also denoted by
lim ( )
x
fx
?8
= ? .
Value Addition: Note
Limits at infinity i.e. the limits of f(x) as x ? ±8 are unique whenever they
exist.
4: Infinite Limits at Infinity:
Let X is a non-empty subset of R and let : X R f ? . Suppose that
00
(, ) X x for x R 8? ? . The function f(x) is said to tends to
() or as x +8 - 8 ? 8 if given any MR ? there exists a number
0
(M) x dd = >
such that for any x d > the function ( ) () () f x M or f x M respectively >< .
Page 4
Limits at Infinity and Asymptotes
Institute of Lifelong Learning, University of Delhi
Lesson: Limits at Infinity and Asymptotes
Course Developer: Brijendra Yadav
Department/College: Assistant Professor, Department of
Mathematics, A.N.D. College, University of Delhi
Limits at Infinity and Asymptotes
Institute of Lifelong Learning, University of Delhi
Table of Contents
Chapter: Limits at Infinity and Asymptotes
• 1: Learning Outcomes
• 2: Introduction
• 3: Limits at Infinity
• 4: Infinite Limits at Infinity
• 5: Limits of Rational Functions at Infinity
• 6: Asymptotes
o 6.1. Horizontal Asymptotes
o 6.2. Vertical Asymptotes
o 6.3. Oblique Asymptotes
o 6.4. Dominant Term of a Function
• Exercises
• Summary
• Reference
1. Learning outcomes:
After studying this chapter you should be able to understand the
? Limits at Infinity
? Infinite Limits at Infinity
? Limits of Rational Functions at Infinity
? Asymptotes
? Horizontal Asymptotes
? Vertical Asymptotes
? Oblique Asymptotes
? Dominant Term of a Function
Limits at Infinity and Asymptotes
Institute of Lifelong Learning, University of Delhi
2. Introduction:
Asymptotes convey the information about the behavior of curves
and determining the asymptotes of a function is an important step in
sketching its graph. In this lesson, we will study about the limits at
infinity and how to use the concept of limits to find the asymptote of a
function.
3: Limits at Infinity:
Let X be any non-empty subset of R, Let : X R f ? . Suppose that
00
(, ) X x for some x R 8? ? . The function f(x) is said to have a limit R ? ? as
x ? 8 if given any 0 e > there exists
0
() x d de = > such that for any x d > ,
then
() fx e -< ?
Limit at infinity is also denoted by
lim ( )
x
fx
?8
= ? .
Value Addition: Note
Limits at infinity i.e. the limits of f(x) as x ? ±8 are unique whenever they
exist.
4: Infinite Limits at Infinity:
Let X is a non-empty subset of R and let : X R f ? . Suppose that
00
(, ) X x for x R 8? ? . The function f(x) is said to tends to
() or as x +8 - 8 ? 8 if given any MR ? there exists a number
0
(M) x dd = >
such that for any x d > the function ( ) () () f x M or f x M respectively >< .
Limits at Infinity and Asymptotes
Institute of Lifelong Learning, University of Delhi
The infinite limit at infinity is denoted by
lim ( ) lim ( )
xx
fx or fx
?8 ?8
= 8 = -8 .
Theorem 1: Let X be a non-empty subset of R and let f(x) and g(x) are
two functions defined on X and suppose that
00
(, ) X x for some x R 8? ? . And
suppose that
0
() 0 g x for all x x > > and that for some ,0 R ?? ?? , we have
()
lim
()
x
fx
gx
?8
= ? .
(I) If 0, lim ( ) lim ( )
xx
then f x if and only if g x
?8 ?8
> =8 =8 ? .
(II) If 0, lim ( ) lim ( )
xx
then f x if and only if g x
?8 ?8
< = -8 = 8 ? .
Proof: Let X be a non-empty subset of R such that
00
(, ) X x for some x R 8? ? and let f(x) and g(x) are two functions defined on
X and
0
() 0 g x for all x x > > and that for some ,0 R ?? ?? , we have
()
lim
()
x
fx
gx
?8
= ? .
Case (I): Let 0, > ? then there exists
10
xx > such that
1
1 () 3
0
2 () 2
fx
for all x x
gx
<< < > ??
?
1
13
() () ()
22
g x f x g x for all x x
? ? ? ?
<< >
? ? ? ?
? ? ? ?
?? (1)
thus from equation (1) it follows that
lim ( ) lim ( )
xx
f x if and only if g x
?8 ?8
=8=8
Case (II): Let 0, < ? then there exists a positive number k > 0 such that k = - ?
thus there exists
20
xx > such that
2
3 () 1
2 () 2
fx
k k for all x x
gx
- < <- >
?
2
31
() () ()
2 2
k g x f x k g x for all x x
?? ??
- < <- >
?? ??
?? ??
(2)
Page 5
Limits at Infinity and Asymptotes
Institute of Lifelong Learning, University of Delhi
Lesson: Limits at Infinity and Asymptotes
Course Developer: Brijendra Yadav
Department/College: Assistant Professor, Department of
Mathematics, A.N.D. College, University of Delhi
Limits at Infinity and Asymptotes
Institute of Lifelong Learning, University of Delhi
Table of Contents
Chapter: Limits at Infinity and Asymptotes
• 1: Learning Outcomes
• 2: Introduction
• 3: Limits at Infinity
• 4: Infinite Limits at Infinity
• 5: Limits of Rational Functions at Infinity
• 6: Asymptotes
o 6.1. Horizontal Asymptotes
o 6.2. Vertical Asymptotes
o 6.3. Oblique Asymptotes
o 6.4. Dominant Term of a Function
• Exercises
• Summary
• Reference
1. Learning outcomes:
After studying this chapter you should be able to understand the
? Limits at Infinity
? Infinite Limits at Infinity
? Limits of Rational Functions at Infinity
? Asymptotes
? Horizontal Asymptotes
? Vertical Asymptotes
? Oblique Asymptotes
? Dominant Term of a Function
Limits at Infinity and Asymptotes
Institute of Lifelong Learning, University of Delhi
2. Introduction:
Asymptotes convey the information about the behavior of curves
and determining the asymptotes of a function is an important step in
sketching its graph. In this lesson, we will study about the limits at
infinity and how to use the concept of limits to find the asymptote of a
function.
3: Limits at Infinity:
Let X be any non-empty subset of R, Let : X R f ? . Suppose that
00
(, ) X x for some x R 8? ? . The function f(x) is said to have a limit R ? ? as
x ? 8 if given any 0 e > there exists
0
() x d de = > such that for any x d > ,
then
() fx e -< ?
Limit at infinity is also denoted by
lim ( )
x
fx
?8
= ? .
Value Addition: Note
Limits at infinity i.e. the limits of f(x) as x ? ±8 are unique whenever they
exist.
4: Infinite Limits at Infinity:
Let X is a non-empty subset of R and let : X R f ? . Suppose that
00
(, ) X x for x R 8? ? . The function f(x) is said to tends to
() or as x +8 - 8 ? 8 if given any MR ? there exists a number
0
(M) x dd = >
such that for any x d > the function ( ) () () f x M or f x M respectively >< .
Limits at Infinity and Asymptotes
Institute of Lifelong Learning, University of Delhi
The infinite limit at infinity is denoted by
lim ( ) lim ( )
xx
fx or fx
?8 ?8
= 8 = -8 .
Theorem 1: Let X be a non-empty subset of R and let f(x) and g(x) are
two functions defined on X and suppose that
00
(, ) X x for some x R 8? ? . And
suppose that
0
() 0 g x for all x x > > and that for some ,0 R ?? ?? , we have
()
lim
()
x
fx
gx
?8
= ? .
(I) If 0, lim ( ) lim ( )
xx
then f x if and only if g x
?8 ?8
> =8 =8 ? .
(II) If 0, lim ( ) lim ( )
xx
then f x if and only if g x
?8 ?8
< = -8 = 8 ? .
Proof: Let X be a non-empty subset of R such that
00
(, ) X x for some x R 8? ? and let f(x) and g(x) are two functions defined on
X and
0
() 0 g x for all x x > > and that for some ,0 R ?? ?? , we have
()
lim
()
x
fx
gx
?8
= ? .
Case (I): Let 0, > ? then there exists
10
xx > such that
1
1 () 3
0
2 () 2
fx
for all x x
gx
<< < > ??
?
1
13
() () ()
22
g x f x g x for all x x
? ? ? ?
<< >
? ? ? ?
? ? ? ?
?? (1)
thus from equation (1) it follows that
lim ( ) lim ( )
xx
f x if and only if g x
?8 ?8
=8=8
Case (II): Let 0, < ? then there exists a positive number k > 0 such that k = - ?
thus there exists
20
xx > such that
2
3 () 1
2 () 2
fx
k k for all x x
gx
- < <- >
?
2
31
() () ()
2 2
k g x f x k g x for all x x
?? ??
- < <- >
?? ??
?? ??
(2)
Limits at Infinity and Asymptotes
Institute of Lifelong Learning, University of Delhi
thus from equation (2) it follows that
lim ( ) lim ( )
xx
f x if and only if g x
?8 ?8
= -8 = 8 .
Example 1: Show that lim
n
x
x for n N
?8
=8? .
Solution: Let ( ) (0, )
n
f x x for x = ?8
Given MR ? , let sup{ 1, } M d =
Then for all x d > , we have
()
n
fx x x M = =>
Since MR ? is arbitrary, it follows that
lim ( ) lim( )
n
xx
fx x
?8 ?8
= = 8.
Example 2: Prove that
( )
1/
lim 0
k
x
x for k
?8
=8> .
Solution: Let
( )
1/
()
k
fx x =
Given any MR ? , let
k
M d =
Now if x d > , then we have
1/ 1/ kk
x M d ==
Thus, it follows that
1/
lim( )
k
x
x
?8
= 8 .
Example 3: Prove that lim ( 1)
x
x
a for a
?8
=8> .
Solution: Let for 0 a > ,
1 a a = + [since a > 1]
?
[] xx
aa = [where [x] denotes integral value of x]
?
[]
(1 )
x
a >+
?
[]
1
x
a >+
?
[] x
a >
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