(2x+y-2z)² 将(2x+y)看作整体

问题描述:

(2x+y-2z)² 将(2x+y)看作整体

(2x+y-2z)²=(2x+y)^2+(2z)^2-2z(2x+y)
=4x^2+4xy+y^2-4xz-2yz