How to prove whether a function is differentiable

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Homework Help Overview

The discussion revolves around proving the differentiability of a function at a point, specifically examining the limit definition of the derivative. Participants are exploring the mathematical formulation of the limit involving the function values at points x+h and x-h.

Discussion Character

  • Mathematical reasoning, Problem interpretation, Assumption checking

Approaches and Questions Raised

  • Some participants attempt to rewrite the limit expression to align with the first principle of derivatives but express difficulty in doing so. There are suggestions to use substitutions to facilitate the proof.

Discussion Status

The discussion is ongoing, with participants providing insights and alternative approaches. Some guidance has been offered regarding rewriting the limit, but there is no explicit consensus on the method to proceed.

Contextual Notes

Participants are working under the assumption that the function is differentiable at the point in question, and there is some uncertainty regarding the correct interpretation of the limit expression. There is also a mention of potential confusion about the equality of the limit to zero.

haha1234
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Homework Statement



Suppose that f is differentiable at x . Prove that ƒ(x)=lim[h→0] [itex]\frac{ƒ(x+h)-ƒ(x-h)}{2h}[/itex]

Homework Equations





The Attempt at a Solution


I think that it may be proved by first principle,but I cannot rewrite the limit into the form of lim[h→0] [itex]\frac{ƒ(x+2h)-ƒ(x)}{2h}[/itex]
So how can I solve this question?
THANKS
 
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You probably mean f'(x). You can rewrite it via u = x-h.
 
haha1234 said:

Homework Statement



Suppose that f is differentiable at x . Prove that ƒ(x)=lim[h→0] [itex]\frac{ƒ(x+h)-ƒ(x-h)}{2h}[/itex]

I assume this is [itex]f'(x) = ...[/itex]

Homework Equations





The Attempt at a Solution


I think that it may be proved by first principle,but I cannot rewrite the limit into the form of lim[h→0] [itex]\frac{ƒ(x+2h)-ƒ(x)}{2h}[/itex]
So how can I solve this question?
THANKS

Use [itex]f(x+h) - f(x-h) = (f(x+h) - f(x)) + (f(x) - f(x-h))[/itex]
 
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pasmith said:
I assume this is [itex]f'(x) = ...[/itex]



Use [itex]f(x+h) - f(x-h) = (f(x+h) - f(x)) + (f(x) - f(x-h))[/itex]

Sorry,but it maybe equals to 0.:confused:
 

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