帮个忙算个题,

问题描述:

帮个忙算个题,
已知2x-y=0,则y(x+y)÷(x的平方-y的平方)的值是?
A.0 B.2 C-2

原式=y(x+y)/(x+y)(x-y)=y/(x-y)=2x/(x-2x)=-2