If the positive integers and are such that and are both perfect squares, prove that both and are both divisible with .
If the positive integers $x$ and $y$ are such that $3x + 4y$ and $4x + 3y$ are both perfect squares, prove that both $x$ and $y$ are both divisible with $7$.
Školjka 
and 
are such that 
and 
are both perfect squares, prove that both 
.