(1⼀3+1⼀4+1⼀5+1⼀6)×(1⼀4+1⼀5+1⼀6+1⼀7)-(1⼀3+1⼀4+1⼀5+1⼀6+1⼀7)-(1⼀4+1⼀5+1⼀6)

2025-03-17 19:37:13
推荐回答(1个)
回答1:

解:原式=(1/3+1/4+1/5+1/6)×(1/4+1/5+1/6+1/7)-(1/3+1/4+1/5+1/6)-(1/4+1/5+1/6+1/7)+1-1
=[(1/3+1/4+1/5+1/6)-1]×[(1/4+1/5+1/6+1/7)-1]-1
=(1/30)×(-101/420)-1
=-101/12600-1
=-12701/12600.