用两种方法计算（x+y+z)(x-y-z)
问题描述：
用两种方法计算（x+y+z)(x-y-z)
答
1.（x+y+z)(x-y-z)=（x+y+z)[x-(y+z)]=x^2-(y+z)^2=x^2-(y^2+2yz+z^2)=x^2-y^2-2yz-z^22..（x+y+z)(x-y-z)=.x(x-y-z)+y(x-y-z)+z(x-y-z)=x^2-xy-xz+xy-y^2-yz+xz-yz-z^2=x^2-y^2-2yz-z^2