若√x+y-1 +y²+6y+9=0,则x-y的值为?

题目

若√x+y-1 +y²+6y+9=0,则x-y的值为?

答案

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