Simple dirichlet function differentiability

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SUMMARY

The discussion focuses on the differentiability of two functions: the Dirichlet function f(x) defined as {x, x rational; 0, x irrational} and g(x) defined as {x^2, x rational; 0, x irrational}. It is established that f(x) is not differentiable at 0 due to the limit of the difference quotient approaching h/0, which is undefined. In contrast, g(x) is differentiable at 0, as the limit of the difference quotient simplifies to lim(h->0) h, which equals 0.

PREREQUISITES
  • Understanding of limits in calculus
  • Familiarity with the concept of differentiability
  • Knowledge of rational and irrational numbers
  • Ability to compute difference quotients
NEXT STEPS
  • Study the properties of the Dirichlet function in detail
  • Learn about the formal definition of differentiability
  • Explore the implications of differentiability on continuity
  • Investigate other examples of functions that are not differentiable at certain points
USEFUL FOR

Students studying calculus, particularly those focusing on real analysis and differentiability concepts, as well as educators seeking to clarify the properties of piecewise functions.

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Homework Statement


f(x) = {x, x rational, 0, x irrational

g(x) = {x^2, x rational, 0, x irrational

Show that f(x) is not differentiable at 0.
Show that g(x) is differentiable at 0


Homework Equations


f'(x) = lim(h->0) f(x+h) - f(x)/h I suppose


The Attempt at a Solution


Just wondering if I'm thinking right. For f(x) the difference quotient becomes h/0 as h-> 0 and with g(x) it becomes lim(h->0) h^2/h = lim(h->0) h = 0?
 
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Just wondering if I'm thinking right. For f(x) the difference quotient becomes h/0 as h-> 0

I suppose you mean h/h?

and with g(x) it becomes lim(h->0) h2/h = lim(h->0) h = 0?"

That's the general idea, but you have to consider the fact that h may be rational or irrational in a careful writeup.
 

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