If it is from Ps Q, We can do like that

來源: jinjing 於 2012-01-02 11:12:38 [] [舊帖] [給我悄悄話] 閱讀數 : (309 bytes)
回答: 有沒有好辦法？ 由 cma 於 2012-01-01 09:00:01

alfa=20d, beta=2d.

From second ,reflects 1 time, the angle increases 2d,so,n=36 the angle is 90d,that means light goes back the same road,the answer shoud be 72. 70,71,also OK,It is about what is first and last...

If it is strict Math, We have to think about the length,it is boring,...

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• 回複：If it is from Ps Q, We can do like that -cma- ♂ 給 cma 發送悄悄話 (7782 bytes) () 01/02/2012 postreply 13:48:33

• dear cma,81is not good. -jinjing- ♀ 給 jinjing 發送悄悄話 (266 bytes) () 01/02/2012 postreply 16:54:15

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