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Title: L'Hopital's Rule
Description: Evaluation of Indeterminate forms of limits. Clear and concise L'Hopital's Rule discussion. Many examples! Mathematical Analysis for College Calculus. Evaluating Limits at Infinity over Infinity or Zero over Zero.

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Unit 1
...

0

Indeterminate Form ∞/∞

f  x
A limit of the form lim
where
x a g  x 
lim f  x    and lim g  x    is called
x a

x a


an indeterminate form of type
...
7
...

ln x
1
...
lim
x  1
x

0
0
 

e x
3
...


L’Hôpital’s Rule
Suppose f and g are differentiable and g '  x   0
near a except possibly at a
...
Then


if the limit on the right side exists or is  
...
7
...

ln x   
1
...
lim
x 0 1  cos x
L
2x
 lim
x 0 sin x
L
2
 lim
x 0 cos x
2

0
0
 
0
0
 

 Arctan x  0 
3
...

If lim f  x    and lim g  x   0 then
x a

x a

the limit is called an indeterminate form of
type   0
...
Write fg as a quotient:
f
fg 
or
1
g
ˆ
2
...


g
fg 
1
f

Example 1
...
3
Evaluate lim x ln x
...


The following are also considered as   
...
7
...


x 1  x  1
x 1
2 
 1
lim 
 2 
  

x 1  x  1
x 1
x 1
0
 lim 2
0
x 1 x  1
 
L
1
 lim
x 1 2 x
1

2

Indeterminate Form of
Type 00, ∞0, and 1∞
For lim  f  x  
x a

g  x

,

1
...
lim f  x    and lim g  x   0

type 

3
...
7
...


x 0

lim x


x 0

Let

x2

00 


yx

x2

ln y  ln x

x2

ln y  x ln x
2

lim ln y  lim x2 ln x



x 0

x 0

ln x
 lim
x 0 1
x2

0  


 

lim ln y  lim x2 ln x



x 0

x 0

0  

ln x

 lim

x 0 1
 
2
x
1
L
x
 lim
x 0  2
x3
2
 x 
 lim   
x 0
 2
0

yx

lim ln y  0


x2

x 0

lim x  lim y


x2

x 0

x 0

 lim e

x 0

e
1

0

ln y

ye

ln y

Evaluating Indeterminate
Forms of Type 00, ∞0, and 1∞
Given lim  f  x  

g  x

x a

1
...
Then ln y  g  x  ln  f  x  
...
Evaluate limln y
...
Use the identity y  e
That is, lim  f  x  
x a

ln y

g  x

to find lim  f  x  
x a

 lim y  lim e
...


Example 1
...
6
x

 2
Evaluate lim 1  
...

 x
 2
ln y  x ln 1  
 x

 2
lim ln y  lim x ln 1  
x 
x 
 x
 2
ln 1  
 x
 lim
x 
1
x
1 2
 2
2 x
1
L
x
 lim
x 
1
x2

   0
0
0
 

2
 2
2 x
1
L
x
 lim
x 
1
2
x
2x
 lim
x  x  2
L
2
 lim
x  1
2
1



 

 2
y  1  
 x

x

lim ln y  2

x 
x

 2
lim 1    lim y
x 
 x  x 
 lim eln y
x 

e

2

Required Exercises

Answer Exercises in TC7
...
7 (1-28) on page 642-643
Exercises 7
...


End of Unit 1
Title: L'Hopital's Rule
Description: Evaluation of Indeterminate forms of limits. Clear and concise L'Hopital's Rule discussion. Many examples! Mathematical Analysis for College Calculus. Evaluating Limits at Infinity over Infinity or Zero over Zero.