(a+b-c)-(b-a-c)去括号后等于多少,

问题描述:

(a+b-c)-(b-a-c)去括号后等于多少,

(a+b-c)-(b-a-c)
=a+b-c-b+a+c
=2a为什么前面括号式子去括号后符号不变?因为-(b-a-c)可以看成是-1×(b-a-c)=-b+a+c