原式=[x(x-zy)-y(x-zy)]-[3x(x-3y)-zy(x-3y)]=(xx-zxy-xy+zyy)-(3xx-9xy-zxy+3zyy)=xx-zxy-xy+zyy-3xx+9xy+zxy-3zyy=-2xx+8xy-2zyy只需按照分配律几步展开,再进行合并,注意前面是负号的要变号.这应该是初中知识,我教...