2x²+xy-y²-4x+5y-6

=2x²+(y-4)x-y²+5y-6

=2x²+(y-4)x-(y-2)(y-3)

=(2x-y+2)(x+y-3)

两个十字相乘法：

-（y²-5y+6) 2x²+(y-4)x-(y-2)(y-3)

y -2 2x -y+2

╳ ╳

y -3 x y-3

2x²+xy-y²-4x+5y-6

=(2x²+xy-y²)-(4x-5y)-6

=(2x-y)(x+y)-(4x-5y）-6

=(2x-y+2)(x+y-3)

也是两个十字相乘法：

2x²+xy-y² (2x-y)(x+y)-(4x-5y）-6

2x -y 2x-y 2

╳ ╳

x y x+y -3