$\begin{array}{l}Chọn\,\,x \in A\backslash(A\backslash B)\\ \to \begin{cases}x \in A\\x \not\in (A\backslash B)\end{cases}\\ \to \begin{cases}x \in A\\x \in B\end{cases}\\ \to x \in (A\cap B) \end{array}$ Trả lời
$\begin{array}{l}Chọn\,\,x \in A\backslash(A\backslash B)\\ \to \begin{cases}x \in A\\x \not\in (A\backslash B)\end{cases}\\ \to \begin{cases}x \in A\\x \in B\end{cases}\\ \to x \in (A\cap B) \end{array}$