Question 28
Find all functions $f$ from the set of all non-negative real numbers to the set of all real numbers such that $f(1) = 1$ and
$$
(f(x+y))^2 \le f(x^2 - 2xy + y^2)
$$
for all real numbers $x$ and $y$ that satisfy the inequality $x + y \ge 0$.
$$
(f(x+y))^2 \le f(x^2 - 2xy + y^2)
$$
for all real numbers $x$ and $y$ that satisfy the inequality $x + y \ge 0$.