a) \(Ư (6) = \left\{ {1;2;3;6} \right\}\),
\(Ư (9) =\left\{ {1;3;9} \right\}\),
\(ƯC (6, 9) = \left\{ {1;3} \right\}\).
b) \(Ư (7) = \left\{ {1;7} \right\}\),
\(Ư (8) = \left\{ {1;2;4;8} \right\}\),
\(ƯC (7, 8) = \left\{ 1 \right\}\).
c) \(Ư (4) = \left\{ {1;2;4} \right\}\),
\(Ư (6) = \left\{ {1;2;3;6} \right\}\),
\(Ư (8) = \left\{ {1;2;4;8} \right\}\),
\(ƯC (4, 6, 8) = \left\{ {1;2} \right\}\).