对于相邻两个数的乘积要敏感,就像2、6、12、20、30、42、56、72、90、110等,
这种数作为分母时候,就要化成两个分数的和或差,此题为差,
1/30+1/42+1/56+1/72+1/90+1/110
=1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10-1/11
=1/5-1/11 =6/55
您好:
1/30+1/42+1/56+1/72+1/90+1/110
=1/5x6+1/6x7+1/7x8+1/8x9+1/9x10+1/10x11
=1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10-1/11
=1/5-1/11
=6/55
如果本题有什么不明白可以追问,如果满意记得采纳
如果有其他问题请采纳本题后另发点击向我求助,答题不易,请谅解,谢谢。
祝学习进步!
1/30+1/42+1/56+1/72+1/90+1/110
=1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10-1/11
=1/5-1/11
=6/55