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Assume X is a metric space, then X and the empty set are both closed and open,
am I correct?
am I correct?
Correct.How do we define closed sets?
A closed set is one that includes all its boundary points,is this definition right?
So, what do you think??which of the following are closed sets?
a){(x,y): x^2+y^2 >=4}
b){(x,y):x^2+y^2<=4}
c){(x,y):x^2+y^2=4}