Proof of Odd functions' Continuity

AI Thread Summary
An odd function g(x) that is right-continuous at x = 0 must also be continuous at that point, with g(0) = 0. To prove this, it is necessary to show that the left-hand limit as x approaches 0 exists and equals the right-hand limit, specifically that lim_{x to 0^{-}} g(x) equals lim_{x to 0^{+}} g(-x). The discussion emphasizes the importance of the epsilon-delta definition of limits in establishing continuity. Participants express challenges in transitioning from concrete to abstract epsilon-delta proofs, highlighting the need for clarity in applying these concepts to odd functions. Ultimately, the proof hinges on the symmetry property of odd functions to demonstrate continuity at x = 0.
bjgawp
Messages
84
Reaction score
0

Homework Statement


If an odd function g(x) is right-continuous at x = 0, show that it is continuous at x = 0 and that g(0) = 0. Hint: Prove first that \lim_{x \to 0^{-}} g(x) exists and equals to \lim_{x \to 0^{+}} g(-x)


Homework Equations





The Attempt at a Solution


Suppose \lim_{x \to 0^{-}} g(x) = M Let \epsilon > 0. We must find \delta > 0 such that whenever -\delta < x < 0, it follows that |g(x) - M | < \epsilon. We know that -x < \delta but relating this to f(-x) is where I'm stuck. Like the other problem I posted, I can't see what the end result is supposed to be. Any help would be very much appreciated!
 
Physics news on Phys.org
I think your attempted solution takes it too far! For an odd function f(-x) = -f(x), that should be enough to get your proof.
 
Hmm I think I do have to incorporate epsilon delta proofs in this one. I was thinking that since -g(x) = g(-x) then |-g(x)| = |g(-x)|. And since we're proving that the limit of odd continuous functions have a limit at 0 (I think that's a safe assumption) then:
Given \epsilon&gt;0. \exists\delta &gt;0 such that whenever 0 < |x| < \delta it follows that |g(x) - M| < \epsilon. Since M = 0, then |g(x)|&lt;\epsilon. (All this is the function approaching 0 from the left)

Then looking at g(-x), for the same epsilon and delta (since the definition of odd functions implies symmetry about the origin) we arrive at the same conclusion |g(x)| < \epsilon.

Do I seem to be on the right track or is this just dead wrong? It's difficult making the transition from concrete, repetitive epsilon-delta proofs to more general and abstract ones. The methods don't quite seem to be the same ...
 
Last edited:
I tried to combine those 2 formulas but it didn't work. I tried using another case where there are 2 red balls and 2 blue balls only so when combining the formula I got ##\frac{(4-1)!}{2!2!}=\frac{3}{2}## which does not make sense. Is there any formula to calculate cyclic permutation of identical objects or I have to do it by listing all the possibilities? Thanks
Essentially I just have this problem that I'm stuck on, on a sheet about complex numbers: Show that, for ##|r|<1,## $$1+r\cos(x)+r^2\cos(2x)+r^3\cos(3x)...=\frac{1-r\cos(x)}{1-2r\cos(x)+r^2}$$ My first thought was to express it as a geometric series, where the real part of the sum of the series would be the series you see above: $$1+re^{ix}+r^2e^{2ix}+r^3e^{3ix}...$$ The sum of this series is just: $$\frac{(re^{ix})^n-1}{re^{ix} - 1}$$ I'm having some trouble trying to figure out what to...
Back
Top