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 furfur233 March 9th, 2019 06:22 AM

Need help with a functional equation

$$f: \mathbb{R} \to \mathbb{R}\qquad \frac{f(x+y)}{x+y} = \frac{f(x)-f(y)}{x-y}, \qquad \forall x,y\in \mathbb{R}, \left|x\right| \neq \left|y\right|$$

 Micrm@ss March 9th, 2019 06:47 AM

Start by filling in some interesting values. For exampe x=0, y=1, ...

 furfur233 March 9th, 2019 07:22 AM

I’ve already tried.. the only thing that results is f(0)=0

 mathman March 9th, 2019 12:29 PM

f(2x)=2xf'(x). Interesting?

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