Answer variants:
Verify \((A \cap B)' = A' \cup B'\) using Venn diagrams.
Proof:
\(A \cap B =\)
\((A \cap B)' =\) ---- (\(1\))
\(A' =\)
\(B' =\)
\(A' \cup B' =\) ---- (\(2\))
From equations (\(1\)) and (\(2\)), we have \((A \cap B)' = A' \cup B'\).
Hence, we proved.