<s>[INST] $x^2-y^2=196$, 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.
 [/INST] Hint 1: $x^2-y^2 = (x+y)(x-y)$.
Hint 2: Divisors of $196$: $1$, $2$, $4$, $7$, $14$, $28$, $49$, $98$, $196$.
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