# A calculus problem by Harnakshvir Singh Dhillon

Calculus Level 4

Let $$f$$ be a differentiable function on the real numbers satisfying, for all real numbers $$x,y$$,

$f(x+y) = f(x) + f(y) + xy$

and $$\lim_{h \to 0} \frac{f(h)}{h} = 3$$. What is the value of $$f(1)$$?

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