若√x+y-1 +y²+6y+9=0,则x-y的值为?

若√x+y-1 +y²+6y+9=0,则x-y的值为?
若√x+y-1 +y²+6y+9=0,则x-y的值为?

若√x+y-1 +y²+6y+9=0,则x-y的值为?
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

√x+y-1 +y²+6y+9=0
变化可得
√（x+y-1）+（y=3）²=0
非负数相加得0，则
x+y-1=0，y+3=0
得x=4，y=-3
则x-y=4-（-3）=4+3=7

√x+y-1 +y²+6y+9=0
√x+y-1 +(y+3)²=0
则必有：
x+y-1=0
y+3=0
解得：x=4；y=-3
x-y=4+3=7