3x^2+4xy+y^2-5x-3y+2
=(3x^2+4xy+y^2)-5x-3y+2
=(3x+y)(x+y)-(3x+y)-2x-2y+2
=[(3x+y)(x+y)-(3x+y)]-2(x+y-1)
=(3x+y)(x+y-1)-2(x+y-1)
=(x+y-1)(3x+y-2)