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Homework Statement
In general, in R^n, what is the best way to approach the problem - a given set is open?
The given set E is such that for all x,y that belong to the given set, d(x,y) < r.
Homework Equations
The Attempt at a Solution
let x be the center of the sphere and y be any point such that d(x,y) < r. Now, let z be any boundary point such that d(x,z) = r.
Also let d(y,z) < epsilon. We can make a neighborhood N with epsilon as radius and y as point such that all points of N are subset of the given set. In general we can construct a neighborhood N of smallest (of all possible neighborhoods with the same center) radius r ,
such that N is a subset of E. Hence, all points of the given open set are internal points. Hence, the given set is open.
Is it an okay proof? Or should I be proving that the complacent of the open set in a given universe is closed. Hence, the set is open?.
I am somewhat new to the method of writing proofs, and so want to know that which is a better way to prove?
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