$x^2-y^2=196$, can we find the value of $x^2+y^2$? $x$ and $y$ are positive integers. 
If $x^2-y^2=196$, can we know what the value of $x^2+y^2$ is?
Can anyone explain this to me? Thanks in advance.

It is possible to find out $x^2+y^2$, as $196$, which will be $(x-y)(x+y)$, can be factorised as five possible integer products, $14\times 14$, $7\times28$, $4\times 49$, $2\times 98$, $1\times 196$. 
Of these only one product leads to both positive and integer solutions for $x$ and $y$. Can you work out which of the products this will be?
