z=3y-2x代入原式,得2x^2+3xy-9y^2+(3y-2x)^2+3x(3y-2x)去括号,原式=2x^2+3xy-9y^2+9y^2-12xy+4x^2+9xy-6x^2 =0
2x^2+3xy-9y^2+z^2+3xz用双十字法分解因式,得:原式=(2x-3y+z)(x+3y+z)∴2x-3y+z=0∴原式=0