Difference between Continuity and Derivatives.

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Discussion Overview

The discussion centers around the concepts of continuity and differentiability in mathematics, exploring their definitions, relationships, and the conditions under which a function can be continuous but not differentiable. Participants examine the limits involved in both concepts and provide examples to illustrate their points.

Discussion Character

  • Conceptual clarification, Debate/contested, Mathematical reasoning

Main Points Raised

  • Some participants express confusion about the relationship between continuity and differentiability, questioning why a continuous function may not be differentiable.
  • One participant notes that the limits used to define continuity and differentiability are different, suggesting this distinction is crucial to understanding their relationship.
  • Another participant provides an example of the function f(x)=|x|, which is continuous at x=0 but not differentiable there, as the derivative differs on either side of the point.
  • A later reply clarifies that while differentiability at a point implies continuity at that point, the reverse is not necessarily true.

Areas of Agreement / Disagreement

Participants generally agree on the definitions of continuity and differentiability, but there remains some confusion and debate regarding their relationship, particularly in cases where a function is continuous but not differentiable.

Contextual Notes

The discussion highlights the importance of understanding the specific limits involved in the definitions of continuity and differentiability, as well as the implications of these definitions for different types of functions.

cjaylee
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Hey. I am quite confused by continuity and derivatives. Both are finding the limits of a particular function as x approaches a. Then why is it that a graph that is continuous cannot be differentiable? If it is continuous, it means that the limit exists and so, it should be differentiable right?
 
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If p is three, does that mean q has to be three as well?

The limits used in the definitions of continuity and differentiability of a function f are different limits.
 
For example, a function with a "point" (f(x)=|x| has a point at x=0) can be continuous but not differentiable since the derivative is different on either side of the point.
 
cjaylee said:
Hey. I am quite confused by continuity and derivatives. Both are finding the limits of a particular function as x approaches a. Then why is it that a graph that is continuous cannot be differentiable? If it is continuous, it means that the limit exists and so, it should be differentiable right?
What "limit exists"? The limit you look at to determine if f(x) is continuous at x= a, is [itex]\lim_{x\to a} f(x)[/itex] while the limit you look at to determine if f(x) is differentiable at x= a is [itex]\lim_{h\to a} (f(a+h)- f(a))/h[/itex]. It is easy to show that if a function is differentiable at x= a, it must be continuous but the other way is not true.
 

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