用两种方法计算(x+y+z)(x-y-z)

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用两种方法计算(x+y+z)(x-y-z)
用两种方法计算(x+y+z)(x-y-z)

用两种方法计算(x+y+z)(x-y-z)
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^2
2..(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