solution

來源: enchanted 於 2009-09-21 21:08:05 [] [舊帖] [給我悄悄話] 閱讀數 : (213 bytes)
本帖於 2009-09-23 04:14:19 時間, 由版主 笑比哭好 編輯
回答: #2: 13.5? 由 coolpang 於 2009-09-21 12:00:35

1:
sqr(2+x)=x
so (2+x)=x*x => x=2 or x=-1

2:
1/3+1/9+1/27+... = x = (2/3-1/3)+(2/9-1/9)+(2/27-1/27)...
=2/3-(1/3-2/9)-(1/9-2/27)-(1/27-...
=2/3-1/9-1/27-1/81=2/3-(x-1/3)
So x=1-x => x=1/2

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• 厲害 -lostman- ♂ 給 lostman 發送悄悄話 (0 bytes) () 09/22/2009 postreply 16:30:14

• 1st is good, 2nd not so good. There is a smarter way for it -朱歌亮- ♂ 給 朱歌亮 發送悄悄話 朱歌亮 的博客首頁 (59 bytes) () 09/22/2009 postreply 20:13:53

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