i think it is closed, if we define a sequence :

i hope my definition of closed subset is right. Maybe my result is wrong coz i choose a special case.

another question ,what about

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- Nov 1st 2008, 06:15 PMszpengchaois this subset of R2 closed or open

i think it is closed, if we define a sequence :

i hope my definition of closed subset is right. Maybe my result is wrong coz i choose a special case.

another question ,what about - Nov 2nd 2008, 03:30 PMCaptainBlack
It is closed because it contains all its limit points. It is not open as there are points in the set which are not in an open ball contained in the set.

Quote:

another question ,what about

CB