real analysis - Finding a counter example to one of four formulas for images and inverse images

So this is a question out of Real Analysis book that I'm working through, and I'm quite stuck.

Give a counterexample to one of the following four formulas for images and inverse images of sets (the other three are true)

1. $f(X_1 \cup X_2) = f(X_1) \cup f(X_2$),


2. $f^{-1}(Y_1 \cup Y_2) = f^{-1}(Y_1) \cup f^{-1}(Y_2)$,


3. $f(X_1 \cap X_2) = f(X_1) \cap f(X_2)$,


4. $f^{-1}(Y_1 \cap Y_2) = f^{-1}(Y_1) \cap f^{-1}(Y_2)$

I went through Overview of basic results about images and preimages and from other resources I can find online, all 4 of these are true... I can't figure out what I am missing.

Thanks for the help

Answer

3 is false, if F is a contant map and $X_1, X_2$ disjoint.
Exercise. Prove for 3 that the
left hand side is a subset of the right hand side.