Is there any direct formula to find the complement of (A-B)?
Hello matsci0000A slightly simpler version of the formula that HallsofIvy has given you is $\displaystyle A' \cup B$, where $\displaystyle A'$ is the complement of $\displaystyle A$ (which is sometimes written $\displaystyle A^c$).
If you know the Laws of Sets, you can prove this as follows:
First, the definition: $\displaystyle A - B = A \cap B'$ (the elements that are in $\displaystyle A$ but not in $\displaystyle B$)
So $\displaystyle (A-B)' = (A \cap B')'$
$\displaystyle = A' \cup (B')'$ (De Morgan's Law)
$\displaystyle = A' \cup B$ (Involution Law)
Grandad