已知(x-y)(x-y-6)+9=0,且x+y=5,求x,y的值
问题描述：
已知(x-y)(x-y-6)+9=0,且x+y=5,求x,y的值
答
(x-y)(x-y-6)+9=0
(x-y)²-6(x-y)+9=0
(x-y-3)²=0
x-y-3=0
x+y=5
相加
2x-3=5
所以
x=4
y=5-x=1