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

来源: jinjing 于 2012-01-02 11:12:38 [] [旧帖] [给我悄悄话] 阅读数 : (309 bytes)
回答: 有没有好办法？ 由 cma 于 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,...

所有跟帖： 

• 回复：If it is from Ps Q, We can do like that -cma- ♂ 给 cma 发送悄悄话 (7782 bytes) () 01/02/2012 postreply 13:48:33

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

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