d2jsp
Log InRegister
d2jsp Forums > Off-Topic > General Chat > Homework Help > Math Proof > Analysis
Add Reply New Topic New Poll
Member
Posts: 167
Joined: Oct 2 2014
Gold: 0.00
Mar 21 2015 07:34pm

i need help proving this. plz show steps. i may pay fg if answer is sufficient. thx
Member
Posts: 12,427
Joined: Mar 4 2006
Gold: 5,077.00
Mar 22 2015 10:16pm
Assume what is given

We know every continuous function is reimann integrable this for x is a member of [0,1]/E our functions is integrable.

Now for x is a member of E. We know every cantor set is uncountable And has lebesgue number 0. We also know since the cantor set is the compliment of the Union of open sets it is closed and bounded. Thus by the lebesgue reimann theorem this is reimann integrable.
Member
Posts: 54,265
Joined: Aug 22 2004
Gold: 6,069.00
Mar 22 2015 10:38pm
Quote (Xx Shin3d0wn xX @ Mar 22 2015 11:16pm)
Assume what is given

We know every continuous function is reimann integrable this for x is a member of [0,1]/E our functions is integrable.

Now for x is a member of E. We know every cantor set is uncountable And has lebesgue number 0. We also know since the cantor set is the compliment of the Union of open sets it is closed and bounded. Thus by the lebesgue reimann theorem this is reimann integrable.


I may be wrong, but isn't there a more elementary proof that doesn't require lebesgue measure/integration?
Member
Posts: 12,427
Joined: Mar 4 2006
Gold: 5,077.00
Mar 23 2015 08:01am
Quote (Casey @ Mar 22 2015 11:38pm)
I may be wrong, but isn't there a more elementary proof that doesn't require lebesgue measure/integration?



I do believe so but I looked at this before bed and couldn't remember if my more elementary proof was correct and I knew this one was.

Here's 2 very elementary approaches:

Pf:
Since [0,1] is a compact set and E is a cantor set which is compact by definition, then the subset [0,1]/E must also be compact since it is the subset of a compact set. Thus f is reimann integrible. Done.

Pf:
Since we know our set of points E is a cantor set which has measure zero and we know f is continuous at every non cantor point then f is reimann integrable. Done.

This post was edited by Xx Shin3d0wn xX on Mar 23 2015 08:06am
Member
Posts: 16,662
Joined: Nov 24 2007
Gold: 15,245.00
Trader: Trusted
Mar 23 2015 06:33pm
Quote (en.wiki)
A function on a compact interval [a, b] is Riemann integrable if and only if it is bounded and continuous almost everywhere (the set of its points of discontinuity has measure zero, in the sense of Lebesgue measure). This is known as the Lebesgue's integrability condition or Lebesgue's criterion for Riemann integrability or the Riemann—Lebesgue theorem.


http://en.wikipedia.org/wiki/Riemann_integral

Since the range of f is [0;1], it is bounded. And as said before, E has measure zero.
Member
Posts: 54,265
Joined: Aug 22 2004
Gold: 6,069.00
Mar 23 2015 08:51pm
Quote (feanur @ Mar 23 2015 07:33pm)
http://en.wikipedia.org/wiki/Riemann_integral

Since the range of f is [0;1], it is bounded.


Cheap but effective way of doing it. Continuous + bounded implies Riemann integrable. Assuming you're allowed to use that theorem. Didn't think of that.

This post was edited by Casey on Mar 23 2015 08:52pm
Go Back To Homework Help Topic List
Add Reply New Topic New Poll