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- - **Need help with a functional equation**
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Need help with a functional equation$$ f: \mathbb{R} \to \mathbb{R}\qquad \frac{f(x+y)}{x+y} = \frac{f(x)-f(y)}{x-y}, \qquad \forall x,y\in \mathbb{R}, \left|x\right| \neq \left|y\right| $$ Can I prove anything interesting about this function? I need to find it. |

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

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

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

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