你题目是不是：
x^2-y^2-6x+9
= (x^2-6x+9)-y^2
=(x-3)^2-y^2
=(x-3+y)(x-3-y)
=(x+y-3)(x-y-3)
如是计算则应是下面,你看看吧
x^2-y^2-6x=9
x^2+6x+9+y^2=0
(x+3)^2+y^2=0
且 (x+3)^2≥0,y^2≥0
所以：(x+3)^2=0 y^2=0
x+3=0 y=0
解得：x=-3 y=0
你题目是不是：
x^2-y^2-6x+9
= (x^2-6x+9)-y^2
=(x-3)^2-y^2
=(x-3+y)(x-3-y)
=(x+y-3)(x-y-3)
如是计算则应是下面,你看看吧
x^2-y^2-6x=9
x^2+6x+9+y^2=0
(x+3)^2+y^2=0
且 (x+3)^2≥0,y^2≥0
所以：(x+3)^2=0 y^2=0
x+3=0 y=0
解得：x=-3 y=0