Limits with sinx where x tends to infinity help.

  • Thread starter Thread starter quackdesk
  • Start date Start date
  • Tags Tags
    Infinity Limits
Click For Summary
SUMMARY

The discussion centers on evaluating the limit of sin(x) as x approaches infinity, where the user incorrectly applies L'Hôpital's Rule multiple times. The correct approach involves recognizing that the expression (1 + cos(x))/(1 - cos(x)) does not present an indeterminate form after the first differentiation, thus L'Hôpital's Rule should not be reapplied. The limit of sin(x)/x as x approaches infinity is zero, and the limit of the original expression does not exist.

PREREQUISITES
  • Understanding of limits in calculus
  • Familiarity with L'Hôpital's Rule
  • Knowledge of trigonometric functions and their properties
  • Ability to identify indeterminate forms
NEXT STEPS
  • Study the application of L'Hôpital's Rule in various scenarios
  • Learn about limits involving trigonometric functions
  • Explore alternative methods for evaluating limits that do not exist
  • Investigate the behavior of sin(x) and cos(x) as x approaches infinity
USEFUL FOR

Students studying calculus, particularly those focusing on limits and trigonometric functions, as well as educators looking for examples of common misconceptions in limit evaluation.

quackdesk
Messages
7
Reaction score
0

Homework Statement


http://prikachi.com/images/26/4273026B.gif


Homework Equations




The Attempt at a Solution


I'm having problems in solving the limit which is shown on the gif file .
As you see I use L'Hopital's rule 2 times and I get to a point when I should divide -sinx with sinx which results in -1 instead of 1 which is the right answer according to the key.

P.S sorry for posting the same thread in another sub-forum before I came here.
 
Physics news on Phys.org
quackdesk said:

Homework Statement


http://prikachi.com/images/26/4273026B.gif


Homework Equations




The Attempt at a Solution


I'm having problems in solving the limit which is shown on the gif file .
As you see I use L'Hopital's rule 2 times and I get to a point when I should divide -sinx with sinx which results in -1 instead of 1 which is the right answer according to the key.

P.S sorry for posting the same thread in another sub-forum before I came here.

You should have stopped after the first differentiation. (1+cos(x))/(1-cos(x)) doesn't have indeterminant form. You can't apply l'Hopital again. And the limit of that expression as x->infinity doesn't exist. So l'Hopital doesn't apply. You'll have to think of another way to find the limit or show one doesn't exist.
 
Solving this limit may help (you can even use l'Hopital's rule!)
lim x->infinity sinx/x
 

Similar threads

  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 19 ·
Replies
19
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 13 ·
Replies
13
Views
3K
  • · Replies 23 ·
Replies
23
Views
2K
  • · Replies 13 ·
Replies
13
Views
3K
  • · Replies 14 ·
Replies
14
Views
3K
  • · Replies 27 ·
Replies
27
Views
29K
  • · Replies 13 ·
Replies
13
Views
2K
  • · Replies 3 ·
Replies
3
Views
1K