Why is cot(x) continious in (0,pi) ?

  • Context: Undergrad 
  • Thread starter Thread starter phymatter
  • Start date Start date
Click For Summary

Discussion Overview

The discussion revolves around the continuity of the cotangent function, cot(x), specifically within the interval (0, π). Participants explore the implications of the behavior of tan(x) near π/2 and how it affects the continuity of cot(x).

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions the continuity of cot(x) at π/2, noting that tan(x) approaches infinity at that point, which leads to the conclusion that cot(x) cannot be continuous since it tends to zero but is never actually zero.
  • Another participant argues that to determine the continuity of cot(x), one must examine the limits of 1/tan(x) from both sides of π/2, suggesting that since both limits approach zero, cot(x) is continuous and takes the value zero.
  • A subsequent reply emphasizes that for continuity at a point, the left-hand limit (LHL), right-hand limit (RHL), and the function value at that point must all be equal, pointing out that cot(π/2) does not exist.
  • Further contributions challenge the assertion that cot(π/2) is zero, clarifying that cot(x) is defined as cos(x)/sin(x) and that at π/2, cot(π/2) is not defined due to cos(π/2) being zero.
  • One participant highlights a misunderstanding regarding the definition of cot(x) as 1/tan(x), stating that this relationship holds only when both functions are defined.

Areas of Agreement / Disagreement

Participants express differing views on the continuity of cot(x) at π/2, with some asserting it is continuous and others arguing it is not due to the undefined nature of cot(π/2). The discussion remains unresolved with competing interpretations.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the behavior of cot(x) at π/2 and the definitions of continuity and limits. The relationship between cot(x) and tan(x) is also a point of contention.

phymatter
Messages
131
Reaction score
0
why is cot(x) continious in (0,pi) ?

why is cot(x) continious in (0,pi) ?
I mean Cot(x)=1/Tan(x) , now at pi/2 , tan(x) tends to infinity => 1/tan(x) tends to 0 , now
1/tan(x) is certainly not = 0 , therefore how can cot(x) be continious ?
 
Physics news on Phys.org


So for values near, but less then pi/2, Tan goes to +infinity; for values near, but greater then pi/2, tan goes to -infinity. What does that mean about the continuity of cot?

In a case like this you need to look at the two limits of 1/tan, one coming from the left, the other the right. If they are equal then cot is continuous. In this case both approach zero, so the function is continuous and has the value zero.
 


Integral said:
So for values near, but less then pi/2, Tan goes to +infinity; for values near, but greater then pi/2, tan goes to -infinity. What does that mean about the continuity of cot?

In a case like this you need to look at the two limits of 1/tan, one coming from the left, the other the right. If they are equal then cot is continuous. In this case both approach zero, so the function is continuous and has the value zero.

for a function to be continious at c LHL= RHL at c and also lim at c = f(c) , but here cot(pi/2) does not exist !
 


How is it not zero?
 


Integral said:
How is it not zero?


cot(pi/2) only tends to 0 , but is never 0! by defination of limit .
 


No, that does not follow and limits have nothing to do with it. cot(x) is defined as "cos(x)/sin(x)". When x= [itex]\pi/2[/itex], [itex]cos(\pi/2)= 0[/itex] and [itex]sin(\pi/2= 1[/itex] so [itex]cot(\pi/2)= 0[/itex].

You seem to be thinking that cot(x)= 1/tan(x) for all x. It isn't- that is only true as long as both cot(x) and tan(x) exist.
 

Similar threads

  • · Replies 9 ·
Replies
9
Views
3K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 14 ·
Replies
14
Views
4K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 27 ·
Replies
27
Views
4K