Re: [高微] 拓撲
※ 引述《mack (腦海裡依然記得妳)》之銘言：
: ※ 引述《y15973 (B.H.Justin)》之銘言：
: : 一題
: : n
: : 若A，B為R 且A、B皆closed
: : 令A+B={ a+b | a屬於A，b屬於B }
: : 試舉一例A+B亦為closed
: A = {(0,0,0,...,0)} is closed
: B = {(0,0,0,...,1)} is closed
: A+B = {(0,0,0,...,1)} is closed
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我是原PO~~~~~
我真的PO錯題目了Q_Q
A+B closed 真的是隨便想都是XDDD
好啦，我要問A、B皆closed
但A+B非closed的情況，跪求眾大幫忙
感謝大家這次小小力鞭而已Q_Q
下次不敢了
至於znmkhxrw版友提供的答案
A={-n：n€N} , B ={n+1/n：n€N}
A+B非closed是因為1/n -> 0 所以open嗎
※ 編輯: y15973 來自: 140.112.252.176 (11/25 00:40)
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