\(\left(xy\right)^2-14xy+49-x^2-y^2=0\)
\(\Leftrightarrow\left(xy\right)^2-12xy+36-\left(x^2+y^2+2xy\right)+13=0\)
\(\Leftrightarrow\left(xy-6\right)^2-\left(x+y\right)^2=-13\)
\(\Leftrightarrow\left(xy-6+x+y\right)\left(xy-6-x-y\right)=-13\)
\(\Leftrightarrow...\)