Limit of tan(x)/x as x approaching zero

  • Context: Undergrad 
  • Thread starter Thread starter terryds
  • Start date Start date
  • Tags Tags
    Limit Zero
Click For Summary

Discussion Overview

The discussion revolves around the limit of tan(x)/x as x approaches zero, exploring various methods to evaluate this limit, including trigonometric identities and the application of L'Hospital's rule. Participants also reference the squeeze theorem and the limit of sin(x)/x.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant suggests starting with the limit definition and asks for guidance on how to proceed from there.
  • Another participant provides hints involving the identity tan(x) = sin(x)/cos(x) and notes that cos(0) = 1.
  • A participant proposes using the squeeze theorem to evaluate the limit of sin(x)/x, stating that L'Hospital's rule will not work in this case.
  • Another participant questions why L'Hospital's rule would not be applicable, seeking clarification.
  • One participant expresses confidence in using the identity to show that lim x->0 tan(x)/x equals 1, but raises concerns about the hint from an external source regarding the limit definition.
  • A later reply mentions that using L'Hospital's rule directly is valid, but notes a potential circular argument if trying to prove that sin'(0) equals the limit of sin(x)/x as x approaches zero.

Areas of Agreement / Disagreement

Participants express differing views on the applicability of L'Hospital's rule in this context, with some asserting it is valid while others contest its use. The discussion remains unresolved regarding the best approach to evaluate the limit.

Contextual Notes

There are unresolved questions about the appropriate identities to use and the conditions under which L'Hospital's rule is applicable. Some participants express uncertainty about the implications of using certain methods.

terryds
Messages
392
Reaction score
13
Physics news on Phys.org
Hints: [itex]tan(x)=\frac{sin(x)}{cos(x)}[/itex] and cos(0) = 1.
 
Furthermore use sqeeze theorem to calculate [tex]\lim_{x\to 0}{\frac{\sin{x}}{x}}[/tex]
L'Hospital rule will not work in that limit
 
Mariuszek said:
L'Hospital rule will not work in that limit
Why not?
 
Svein said:
Hints: [itex]tan(x)=\frac{sin(x)}{cos(x)}[/itex] and cos(0) = 1.

I know that I can make it lim x->0 tan(x) / x = lim x->0 1/cos(x) * sin(x)/x = 1 * 1 = 1

But, the hint in http://math.stackexchange.com/quest...-lim-limits-x-to0-frac-tan-xx-1#answer-448210 says

lim x->0 tan(x)/x = lim x->0 tan(x)-tan(0)/ x-0
If I plug x=0, the denominator will be zero.
Then, how to solve it using that hint ?
What trigonometric identity should be used ?
 
terryds said:
What trigonometric identity should be used ?
Well, using l'Hôpital directly, you get...
 
  • Like
Likes   Reactions: terryds
Mariuszek said:
Furthermore use sqeeze theorem to calculate [tex]\lim_{x\to 0}{\frac{\sin{x}}{x}}[/tex]
L'Hospital rule will not work in that limit
Sure it will.
##\lim_{x \to 0}\frac{sin(x)}{x} = \lim_{x \to 0}\frac{cos(x)}{1} = 1##
 
Mark44 said:
Sure it will.
##\lim_{x \to 0}\frac{sin(x)}{x} = \lim_{x \to 0}\frac{cos(x)}{1} = 1##

L'Hopital's rule does indeed work here, with the caveat that the argument is circular if you are trying to prove that [itex]\sin'(0) = \lim_{x \to 0} \frac{\sin x}x[/itex] exists and is equal to 1.
 

Similar threads

Replies
3
Views
1K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 8 ·
Replies
8
Views
3K
  • · Replies 19 ·
Replies
19
Views
6K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 3 ·
Replies
3
Views
4K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 9 ·
Replies
9
Views
3K