# Inverse image and continuity

1. Apr 1, 2008

### im2fastfouru

1. a) Show that (f^-1 S)compliment = f^-1(S compliment) for any set S of reals.

Then use part a) to show The function f is continuous iff f^-1(S) is closed for every closed set S.

2. inverse image = f^-1(S) = {x: f(x) $$\in$$ S}
f is continous iff for every open set U $$\in$$ the reals, f^-1(U) is open.

2. Apr 1, 2008

### ircdan

part a is true for any set, so you need to show f^-1(S^c) = (f^-1(S))^c,

so take x in f^-1(S^c), so f(x) is in S^c, so f(x) is not in S, so ...

for part b, what have you tried and what is your definition of continuous, delta/epsilon?