Recent content by plweber

I got it! This is for: if D is an interval that is not open, then f(D) is an interval that is not open. Take f:D->Reals f(x)=(x*sin(x))+x+(1/x) D=[1,infinity) which is not open f(D)=(0,infinity) which is open Woot! Woot! Patrick South Dakota State University - Real Analysis I

That function would have f(D)=(-infinity,infinity) or, in other words, the reals. This interval is both open and closed so it is not a counterexample.