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我有2條proof唔知岩唔岩~~
1. prove  {a} is not an open set
2. prove (a,b] is not an open set
我的做法如下



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IMG-20171011-WA0000.jpeg(167.43 KB)

2017-10-11 03:26 PM

IMG-20171011-WA0000.jpeg

IMG-20171011-WA0002.jpeg(129.02 KB)

2017-10-11 03:26 PM

IMG-20171011-WA0002.jpeg

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1.
There exists a in S={a} such that for all open neighbourhood N of a,
N is not a subset of S.

2.
There exists b in S=(a,b] such that for all open neighbourhood N of b,
N is not a subset of S.



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思路正確, 但係你兩題寫到一舊舊咁又撞晒notation, 稱唔上係正確既數學證明


頹廢

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