1.【2x二次方y(x-y)-x二次方y(x-y)】乘1/x二次方y
=x二次方（x-y）乘1/x二次方y
=x-y
=4
2.【4x二次方+4xy+y二次方-y二次方-4xy-8x】乘1/2x
=（4x二次方-8x）乘1/2x
=4x（x-2）乘1/2x
=2x-4
=16
3.【x二次方-2xy+y二次方+x二次方-y二次方】乘1/2x
=（2x二次方-2xy）乘1/2x
=2x（x-y）乘1/2x
=x-y
=4.5
4.a二次方-1+a-a二次方
=a-1
=2011
像第四提那么简单不要随便问人 省得丢人