Question 152
Let $a$ and $b$ be positive integers such that $a \gt b$ and
$$
a - b = 5b^2 - 4a^2.
$$
Prove that $a-b$ is a square of some positive integer. (Gazeta Matematică 2016)
$$
a - b = 5b^2 - 4a^2.
$$
Prove that $a-b$ is a square of some positive integer. (Gazeta Matematică 2016)