(1⼀4+1⼀5+1⼀6+1⼀7)的平方-(1⼀4+1⼀5+1⼀6+1⼀7)乘(1⼀5+1⼀6+1⼀

2025-03-18 04:30:53
推荐回答(1个)
回答1:

解:(1/4+1/5+1/6+1/7)^2-(1/4+1/5+1/6+1/7)*(1/5+1/6+1/7)
=(1/4+1/5+1/6+1/7)(1/4+1/5+1/6+1/7-1/5-1/6-1/7)
=309/420*1/4
=309/1680