把(x-y)看作一个整体,合并同类项:5(x-y)+2(x-y)-4(x-y)=______.
5(x-y)+2(x-y)-4(x-y)=(5+2-4)(x-y)=3(x-y).
一个六棱柱有( )个面、( )条棱和( )个顶点.
银行卡可以通过电话银行修改初始密码。()