you are so smart! how did you get x[2]=5?

I use generalizing...

X[n+1]- X[n]= 2(X[n]- X[n-1])

thus,

X[n+1]- X[n]
=2*2(X[n-1] - X[n-2])
=2^3(X[n-2] - X[n-3])
=2^4(X[n-3] - X[n-4])
....
=2^(n-1)(X[2] - X[1])

for X1=3 Thus, X2=???


for n=19, X[20]-X[19] = 2^19(?-3)

所有跟帖： 

• 飛鷹同學，初二沒過關? 還不信我老師 -23731241- ♂ (0 bytes) () 01/10/2010 postreply 16:24:28

• haha, but I still don't know why x2=5:( -戲雨飛鷹- ♀ (0 bytes) () 01/10/2010 postreply 16:26:22

• correction: for n=19, X[20]-X[19] = 2^18(5-3) =2^19 -戲雨飛鷹- ♀ (0 bytes) () 01/10/2010 postreply 16:28:00

• sweetie, sweetie -bearsback- ♂ (44 bytes) () 01/10/2010 postreply 16:56:42

• 題目隻是給出x1=3, sequence,x[n+1]=2x[n-1], -戲雨飛鷹- ♀ (29 bytes) () 01/10/2010 postreply 16:58:21

• 回複：題目隻是給出x1=3, sequence,x[n+1]=2x[n-1], -bearsback- ♂ (35 bytes) () 01/10/2010 postreply 17:02:58

• 隻能是這樣了。要不就缺少條件了。不過， -戲雨飛鷹- ♀ (36 bytes) () 01/10/2010 postreply 17:08:38

• very true. -bearsback- ♂ (55 bytes) () 01/10/2010 postreply 17:30:00

• 考你一個難的（也很簡單）: -戲雨飛鷹- ♀ (59 bytes) () 01/10/2010 postreply 17:34:19

• 兩個2? -bearsback- ♂ (0 bytes) () 01/10/2010 postreply 17:36:55

• 回複：考你一個難的（也很簡單）: -bearsback- ♂ (22 bytes) () 01/10/2010 postreply 17:37:48

• 可以是任何操作，不局限在+－＊／ -戲雨飛鷹- ♀ (0 bytes) () 01/10/2010 postreply 17:40:16

• 回複：可以是任何操作，不局限在+－＊／ -bearsback- ♂ (64 bytes) () 01/10/2010 postreply 17:42:20

• wow!!!!!!!!!!!!!!!!!!!!!!!!! 佩服死了！ -戲雨飛鷹- ♀ (0 bytes) () 01/10/2010 postreply 17:44:26

• because of your hint (any operation) -bearsback- ♂ (0 bytes) () 01/10/2010 postreply 17:45:51

• 天才！我是看答案才知道的。88~~ -戲雨飛鷹- ♀ (0 bytes) () 01/10/2010 postreply 17:49:44

• sweetie, love makes me -bearsback- ♂ (70 bytes) () 01/10/2010 postreply 17:53:37

• 這是IBM一月（趣味智力）：二二得五 -戲雨飛鷹- ♀ (120 bytes) () 01/10/2010 postreply 18:01:10

• sweetie, ibm, hp, apple etc are not my type of company -bearsback- ♂ (23 bytes) () 01/10/2010 postreply 18:07:57

• haha，good one！"company"用的絕妙。 -戲雨飛鷹- ♀ (0 bytes) () 01/10/2010 postreply 18:31:11

• 裏麵的這個答案有點勉強：用exp運算 -戲雨飛鷹- ♀ (66 bytes) () 01/10/2010 postreply 19:05:36

• 回複：裏麵的這個答案有點勉強：用exp運算 -bearsback- ♂ (34 bytes) () 01/10/2010 postreply 19:21:07

• i'm wrong. the value of exp(log2) id not 10:) -戲雨飛鷹- ♀ (0 bytes) () 01/10/2010 postreply 19:29:45

• sweetie, your thinking is inspiring though the value is not ten -bearsback- ♂ (0 bytes) () 01/10/2010 postreply 20:16:07

• no, I copied the answer from 腦壇to show you. after posting -戲雨飛鷹- ♀ (38 bytes) () 01/10/2010 postreply 20:21:28

• oops, l meant left shift -bearsback- ♂ (52 bytes) () 01/10/2010 postreply 17:45:07

• 沒關係，左右兩個坑都要用：）：） -戲雨飛鷹- ♀ (0 bytes) () 01/10/2010 postreply 17:52:01

• hahhaha, that 坑 is the most important -bearsback- ♂ (17 bytes) () 01/10/2010 postreply 17:55:47

• 需要hint和話，說一聲。 -戲雨飛鷹- ♀ (0 bytes) () 01/10/2010 postreply 17:43:08

• 密碼，這個題目對你來講太簡單了。 -戲雨飛鷹- ♀ (0 bytes) () 01/10/2010 postreply 17:37:56