Question 98
Let $a$ and $b$ be two integers with $a \gt b$. If $ab - 1$ and $a+b$ are relatively prime, and $ab + 1$ and $a-b$ are relatively prime, prove that
$$
(ab + 1)^2 + (a - b)^2
$$
is not a perfect square.
$$
(ab + 1)^2 + (a - b)^2
$$
is not a perfect square.