Limit of a function as x goes to 1

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Discussion Overview

The discussion revolves around finding the limit of the function f(x) = (1 - cos(x-1)) / (x-1)² as x approaches 1. Participants explore various methods to evaluate this limit, specifically seeking alternatives to L'Hospital's rule.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Homework-related, Mathematical reasoning

Main Points Raised

  • One participant expresses confusion about the limit and mentions that they know the answer is 1/2, but struggles with their approach.
  • Another participant suggests using a series expansion for the cosine function to simplify the limit calculation, providing a Taylor series expansion as a potential method.
  • A different participant points out that there are missing brackets in the numerator, indicating a possible error in the formulation of the limit.
  • Some participants agree that a Taylor series expansion is a suitable method for solving the limit problem.
  • One participant requests clarification on how to express cos(x-1) as a Taylor series around x=1, indicating a need for further explanation of the series expansion process.

Areas of Agreement / Disagreement

There is a general agreement among participants that a Taylor series expansion is a viable method for evaluating the limit. However, there remains uncertainty regarding the correct application of this method and the initial formulation of the function.

Contextual Notes

Participants have not fully resolved the issue of missing brackets in the numerator, and there is some ambiguity regarding the application of Taylor series and the assumptions involved in the expansion.

Who May Find This Useful

This discussion may be useful for students or individuals seeking to understand limit evaluation techniques, particularly those interested in Taylor series and alternative methods to L'Hospital's rule.

nothingkwt
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f(x) = 1-cos(x-1) / (x-1)2

Can someone please explain how this can be done other than L'Hospital's rule? I tried but I just don't understand how. I know the answer is 1/2 though.

I tried separating to 2 limits but i got ∞ - ∞ and that is obviously wrong but I don't know what my mistake was.
 
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You could do this by doing a series expansion for the numerator and looking at the limit of the leading order expression. This is a useful series expansion:

cos(x-1) ≈ 1 - (x-1)2/2! + (x-1)4/4! + ...
This is basically the definition of cosine, but you can get it through taylor expansion about x=1. Note that as x goes to 1, the higher order terms are negligible.
If you plug this into the numerator of your expression, you get some nice cancellation happening.
 
There are brackets missing for the numerator, I think.

If you know good upper and lower estimates for cos() around 0, you can use them. The full taylor series is the better solution, if you can use that.
 
A Taylor's Series expansion seems to me to be the way to go.
 
Mark44 said:
A Taylor's Series expansion seems to me to be the way to go.

How would you go about even expressing that as a taylor series o.O
 
iRaid, can you express cos(x-1) as a Taylor series around x=1?

Actually Jolb has it above, but it doesn't do much if you don't know why that is what it is.
 

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