Boundary of a ball
Show that the open ball $B(0,1) = \{(x,y): x^2 +y^2 < 1\}$ has the
boundary $x^2+y^2=1$. I understand that the boundary is the closure of the
ball minus the interior. So, if i can show that the closure of the ball is
less than or equal to one, then i would essentially be done, but im not
sure how to do this. I know the closure contains the limit points of the
set, but im not sure how to use this to help me prove what the closure of
the ball is.
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