\(2xy-x^2-y^2+36\)
\(=-\left(x^2+2xy-y^2\right)+36\)
\(=-\left(x^2-2xy+y^2\right)+36\)
\(=-\left(x-y\right)^2+6^2\)
\(=-\left(x-y+6\right).\left(x-y-6\right)\)
Ta có: \(2xy-x^2-y^2+36=-\left(x^2-2xy+y^2-36\right)\)
\(=-\left[\left(x-y\right)^2-36\right]=-\left(x-y-6\right)\left(x-y+6\right)\)