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Only briefly continuous (Posted on 2005-12-15) Difficulty: 2 of 5
Name a function with a domain of all real numbers that is continuous only at a single point.

Definition: A function is continuous at point B if and only if the limit of f(x) as x approaches B is equal to f(B).

  Submitted by Tristan    
Rating: 3.5000 (2 votes)
Solution: (Hide)
f(x) = { x2 if x is rational
       { 0 if x is irrational
This function is related to the Dirichlet function, which is equal to 0 for rationals and 1 for irrationals. The Dirichlet function is never continuous, but here, f(x) is continuous at 0 and only 0.

The particular function I chose is also differentiable only at the single point x=0.

Comments: ( You must be logged in to post comments.)
  Subject Author Date
Some ThoughtsPuzzle AnswerK Sengupta2023-11-25 06:51:25
re(4): Another thoughtgoFish2005-12-17 10:37:54
re(3): Another thoughtLarry2005-12-17 09:41:08
re(2): Another thoughtgoFish2005-12-16 03:13:40
SolutionFunction namedMindRod2005-12-15 23:32:10
Hints/Tipsre: Another thoughtMindRod2005-12-15 23:28:16
Another thoughtLarry2005-12-15 20:46:51
re: Non-piecewiseRichard2005-12-15 14:57:49
QuestionNon-piecewiseJer2005-12-15 14:34:42
See AlsoRichard2005-12-15 12:45:27
SolutionAnother solutionFederico Kereki2005-12-15 09:44:28
A solutiongoFish2005-12-15 08:19:35
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