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What is this property called? The domain and codomain of the function can be for example $\mathbb Z^n$, $\mathbb Q^n$ or $\mathbb R^n$ ($n>0$), potentially excluding the $0$ point. Examples: $f(x)=ax^k$ ($k$ being an odd integer), rotation in the plane around the origin by a fixed angle, $f(x)=\operatorname{sgn}(x)g(|x|)$ (where $g$ is some other function), etc.
I'm thinking of calling it "symmetric around $0$", does that sound right?

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Odd function. Google it. –  DonAntonio Jan 1 at 16:02
    
I posted an answer which clarify the definition. –  Sami Ben Romdhane Jan 1 at 17:11

2 Answers 2

up vote 3 down vote accepted

We call it odd function.

P.S. We call a function which satisfies $f(-x)=f(x)$ even function.

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The oddest of all functions are those that are both even and odd. –  Harald Hanche-Olsen Jan 1 at 16:05
    
Thanks for pointing it out. –  mathlove Jan 1 at 16:06
    
Why the Japanese wikipedia? :) –  aditsu Jan 1 at 16:07
    
Oh, sorry, no meaning! –  mathlove Jan 1 at 16:08
    
I edited it to English one. –  mathlove Jan 1 at 16:09

Just to clarify the definition:

A function defined on a domain $D$ is called odd function if:

  • $-x\in D$ whatever $x\in D$
  • $f(-x)=-f(x)\;\;\forall x\in D$

Notice that the first point is very important although it is often omitted. For example the function $$f\colon [0,\pi]\rightarrow\mathbb R,\quad x\mapsto\sin x$$ isn't an odd function since the first point isn't fullfiled.

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