# Thread: Images of Compact and Connected Sets

1. ## Images of Compact and Connected Sets

Does anybody know an example of a continous map F: R --> R and a closed Subset B C R such that f(b) is not closed.

2. No, because by definition every continuous image of an open set is open, whence every continuous image of a closed set is closed.

3. Originally Posted by mathisnotforme101
Does anybody know an example of a continous map F: R --> R and a closed Subset B C R such that f(b) is not closed.
Let $f(x)=\frac{1}{1+x^2}$ and $B=[0,\infty).$ It is clear that B is a closed set, whereas $f(B)=(0,1]$ is not closed.

4. Originally Posted by julien
No, because by definition every continuous image of an open set is open, whence every continuous image of a closed set is closed.
Julien, you have the definition backward. The inverse image of an open set under a continuous function is open. Likewise, the inverse image of a closed set under a continuous function is also closed.
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