What Distinguishes the Existence of lim_{x \rightarrow x_0} f'(x) from f'(x_0)?

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SUMMARY

The discussion clarifies the distinction between the existence of the limit lim_{x \rightarrow x_0} f'(x) and the existence of f'(x_0). Specifically, it states that the limit can exist even if the function is not continuous at x_0, as demonstrated by the example f(x) = x² for x ≠ 1 and f(1) = 2. In this case, lim_{x \rightarrow 1} f'(x) equals 2, while f'(1) does not exist due to the discontinuity at that point. This highlights that continuity is not a prerequisite for the existence of a limit of the derivative.

PREREQUISITES
  • Understanding of limits in calculus
  • Knowledge of derivatives and their definitions
  • Familiarity with continuity and its implications in calculus
  • Basic proficiency in piecewise functions
NEXT STEPS
  • Study the properties of limits in calculus
  • Explore the concept of continuity and its role in differentiability
  • Investigate piecewise functions and their derivatives
  • Learn about the implications of discontinuities on limits and derivatives
USEFUL FOR

Students studying calculus, particularly those focusing on the concepts of limits, derivatives, and continuity. This discussion is beneficial for anyone seeking to deepen their understanding of the relationship between these fundamental concepts in mathematical analysis.

kittybobo1
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Homework Statement



I had a quick question concerning some definitions. What is the difference between lim_{x \rightarrow x_0} f'(x) to exist and for f'(x_0) to exist, definition wise?

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The Attempt at a Solution

 
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If the function is continuous then the limit as x approaches y of f is equal to f evaluated at y. Continunity is not a required property of derivatives (there are examples to show this).
 
To take a very simple example, let f(x)= x2 if x is not 1, f(1)= 2. For any x other than 1, f(x)= x2 in some interval around 1 and so it's derivative is 2x. limit as x goes to 1 of f'(x) is 2. But since f(x) is not continuous at x= 1, it is not differentiable there.
 

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