Differentiable / continuous functions

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SUMMARY

The discussion centers on constructing a function f: R --> R that is differentiable n times at 0 and discontinuous everywhere else. The proposed function is defined as f(x) = x^(n+1) for rational x and f(x) = 0 for irrational x. The participant confirms the differentiability of this function at 0 and questions whether inverting the definitions would yield the same properties. The consensus is that the function remains differentiable at 0 regardless of the inversion of rational and irrational assignments, but the function f(x) = x^n does not satisfy the conditions required.

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  • Understanding of differentiable functions and their properties
  • Knowledge of rational and irrational numbers
  • Familiarity with limits and continuity in real analysis
  • Basic experience with mathematical notation and function definitions
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  • Study the implications of differentiability and continuity on function behavior
  • Learn about the construction of functions with specific differentiability conditions
  • Investigate the role of rational and irrational numbers in function definitions
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jem05
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Homework Statement


give an example of a function f: R --> R that is differentiable n times at 0, and discontinous everywhere else.

Homework Equations


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The Attempt at a Solution



i got one, and i proved everything, i just want to make sure what i did is correct:

f:x n+1 when x is rational
0 when x is irrational

by the way, does the example hold if i invert them, that is 0 if rational and xn+1 if irrational?
(nothing changes right?)
thank you

oh, and x^n does not work, instead of x^n+1, right?
 
Last edited:
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jem05 said:

Homework Statement


give an example of a function f: R --> R that is differentiable n times at 0, and discontinous everywhere else.

Homework Equations


---

The Attempt at a Solution



i got one, and i proved everything, i just want to make sure what i did is correct:

f:x n when x is rational
0 when x is irrational

btw, does the example hold if i invert them, that is 0 if rational and xn if irrational? (nothing changes right?)
thank you
Your function is differentiable (and hence continuous) everywhere on R, except at a finite number of points. Indeed, your function is differentiable on at least \mathbb{R}\setminus\mathbb{Q}.
 
Last edited:

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