a-(b+c-d)去括号
问题描述：
a-(b+c-d)去括号
a-(b+c-d)= a+5(b+2c-3d)= a-m(b+2c-3d)=
去括号
答
a-(b+c-d)
=a-b-c+d
a+5(b+2c-3d)
=a+5b+10c-15d
a-m(b+2c-3d)
=a-mb-2mc+3md