# Unusual Functional Twist

Algebra Level 5

$\large{f(x+y) = f(x) + 2xy + f(y)}$

Let $f: \mathbb Q \to \mathbb R$ be a function defined on the set of all rational numbers $\mathbb Q$ satisfying the above functional equation for all $x,y \in \mathbb Q$ and where $f(1) = 2015$. Submit the value of $f(20.15)$ upto three correct places of decimals as your answer.

Bonus : Generalize $f(x)$.

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