So you're actually solving √y=√x2=9 .
Ignore √x2, then the equation would be √y=9 .
Now take the left and right sides to the power of 2, so y=81
Now ignore √y and take √x2 in the equation again.
√x2=9, it applies that √x2=x, then x=9 ,
so
x = 9 ,
y = 81,
x and y are positive integers.