1. ## Set Theory Help

prove that:

A^c ∩ B^c ⊆ (A U B)^c

thank you

2. first of all is c an element or a set?

3. sorry...i didnt know how to type the complement sign...

4. Assume $x \in A^-1 \cap B^-1 .$ By Def, $x \notin A$ and $x \notin B$ so $x \in (U-A-B)$ which means $x \in U - (A + B) = (A \cup B)^{-1}$ remember the distributive laws work on sets.