6/7-6/7×﹙2/3+9/2﹚简便方法,

问题描述:

6/7-6/7×﹙2/3+9/2﹚简便方法,
2/9改成1/9

6/7-6/7×﹙2/3+1/9﹚
=6/7×﹙1-2/3-1/9﹚
=6/7×2/9
=4/21为什么括号里要变减减去两个数的和=分别减去这两个数。a-(b+c)=a-c-b5个1/5之间添符号,怎么得3(1/5+1/5)÷1/5+1/5÷1/5=3