|a-b| +|a|=_____(化简）x-xy=20,xy-y=-10,x-y=____,x+y-2xy=_____.
问题描述：
|a-b| +|a|=_____(化简）x-xy=20,xy-y=-10,x-y=____,x+y-2xy=_____.
答
=a-b+a=2a-b或=b-a+a=b
x-xy+xy-y=x-y=10
x+y-2xy=x-xy-(xy-y)=30