Question 50
Let $\mathbb{R}$ denote the set of all real numbers. Find all possible functions $f : \mathbb{R} \to \mathbb{R}$ such that:
for all real numbers $x, y$, $f(f(x) + y) = f(x^2 - y) + 4(y - 2)(f(x) + 2)$.
for all real numbers $x, y$, $f(f(x) + y) = f(x^2 - y) + 4(y - 2)(f(x) + 2)$.