求什么?就是拆括号吗?如果只是拆括号,就是:
(2x+y-z)^2=(2x+y-z)*(2x+y-z)
=4x^2+2xy-2xz+2xy+y^2-yz-2xz-yz+z^2
=4x^2+y^2+z^2+4xy-4xz-2yz