x(x-y-z)-y(y-x+z)-z(z-x+y),
=x(x-y-z)+y(x-y-z)+z(x-y-z)
=(x-y-z)(x+y+z)为啥x(x-y-z)+y(x-y-z)+z(x-y-z)=(x-y-z)(x+y+z) ？脑子现在转不过弯来……提取公因式（x-y-z)