# Another Functional Equation 3

Algebra Level 4

$\large{f(x-y) = f(x) + xy + f(y)}$

Let $$f: \mathbb R \to \mathbb R$$ be a function satisfying the above functional equation for every $$x \in \mathbb R$$. Then find the value of $$f(20.15)$$ to three places of decimals.

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