若√x+y-1 +y²+6y+9=0,则x-y的值为?
问题描述：
若√x+y-1 +y²+6y+9=0,则x-y的值为?
答
若√x+y-1 +y²+6y+9=0
若√x+y-1 +(y+3)²=0,则x-y的值为
x+y-1=0
y+3=0
y=-3
x=4
则x-y=4-(-3)=7