1. If (a+1/a)二次方=7,find the value of a二次方+1/a二次方
2. Evaluate 1/1x2+1/2x3+1/3x4+...+1/49x50
要有答案,最好有WHY(唔要都得),謝
F.1 2條奧數題,急
2010-12-18 2:41 am
回答 (1)
2010-12-18 3:00 am
✔ 最佳答案
1. (a+1/a)^2 = a^2 + 2 a(1/a) + (1/a)^2 = a^2+(1/a)^2 + 2 = 7So, a^2 + (1/a)^2 = 5
2. 1/1x2 + 1/2x3 + ...+ 1/49x50
=(1-1/2) + (1/2 - 1/3) + .... + (1/48 - 1/49) + (1/49 - 1/50)
= 1 - 1/50 = 49/50
收錄日期: 2021-04-23 21:34:55
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https://hk.answers.yahoo.com/question/index?qid=20101217000051KK00723