- Thread starter
- #1
Hi dwsmith,$(A - B)\cup B = A$ iff $B\subseteq A$.
Suppose $B\subseteq A$.
$$
\begin{array}{lcl}
(A - B)\cup B & = & (A\cap B^c)\cup B\\
& = & (A\cup B)\cap (B^c\cup B)\\
& = & A\cap B\\
& = & B
\end{array}
$$
I keep getting = B not A.