2x^2+3xy-9y^2-7x+6y+3
=2x^2+(3y-7)x-(9y^2-6y-3)
=2x^2+(3y-7)x-3(3y^2-2y-1）
=2x^2+(3y-7)x-3(3y+1)(y-1)
=(x+3y-3)(2x-3y-1)