Re: [計量] 今日計量考題
what is the least possible value of 3^x+3*3^(-x)
選項有
(A)1 (B)2 (C)3 (D)3.5 (E)4
我是這樣想啦:
3^x + 3*3^(-x)
= 3^x + 3^(1-x)
當x=1/2時加號兩邊相等,代入後為2*3^0.5 ,也是頂點
3^2 < (2*3^0.5)^2 < 3.5^2 → 9 < 12 < 12.25
所以要嘛就是abc不可能,不然就de不可能
又發現當x=1or0時,代入得到4
所以abc不可能 ...是多選吧o'_'o|||不然我就糗大了
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※ 文章網址: http://www.ptt.cc/bbs/GRE/M.1414864697.A.36C.html
※ 編輯: worm6206 (59.115.222.69), 11/02/2014 02:02:15
→
11/02 08:27, , 1F
11/02 08:27, 1F
→
11/02 08:27, , 2F
11/02 08:27, 2F
推
11/02 08:54, , 3F
11/02 08:54, 3F
→
11/02 08:54, , 4F
11/02 08:54, 4F
→
11/02 10:47, , 5F
11/02 10:47, 5F
我也是會選D, 因為題目least possible value解讀為「最小可能值」的話
D自然比E好
※ 編輯: worm6206 (59.115.204.74), 11/02/2014 10:59:29
→
11/02 18:53, , 6F
11/02 18:53, 6F
→
11/02 18:53, , 7F
11/02 18:53, 7F
推
11/02 21:47, , 8F
11/02 21:47, 8F
→
11/02 23:47, , 9F
11/02 23:47, 9F
如果有x是整數,E自然是解
看來原po題目沒看清楚 (o'_'o)σ
※ 編輯: worm6206 (59.115.204.74), 11/03/2014 00:23:45
→
11/03 03:40, , 10F
11/03 03:40, 10F
→
11/03 03:40, , 11F
11/03 03:40, 11F
→
11/03 15:32, , 12F
11/03 15:32, 12F
→
11/03 15:33, , 13F
11/03 15:33, 13F
推
11/03 16:51, , 14F
11/03 16:51, 14F
→
11/03 16:52, , 15F
11/03 16:52, 15F
→
11/03 18:17, , 16F
11/03 18:17, 16F
那應該代入 0 1 2 之後就可以選E了
※ 編輯: worm6206 (59.115.204.74), 11/03/2014 20:27:17
→
11/04 02:00, , 17F
11/04 02:00, 17F
→
11/04 02:06, , 18F
11/04 02:06, 18F
→
11/04 02:17, , 19F
11/04 02:17, 19F
→
11/04 02:18, , 20F
11/04 02:18, 20F
→
11/04 02:18, , 21F
11/04 02:18, 21F
→
11/04 02:19, , 22F
11/04 02:19, 22F
→
11/04 02:20, , 23F
11/04 02:20, 23F
→
11/04 02:20, , 24F
11/04 02:20, 24F
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