\(a)\) \(Ư(8) = \left\{ {1;2;4;8} \right\}\)
\(Ư(12) = \left\{ {1;2;3;4;6;12} \right\}\)
\(ƯC(8; 12) = \left\{ {1;2;4} \right\}\)
\(b)\) \(B(8) = \left\{ {0;8;16;24;32;48;...} \right\}\)
\( B(12) = \left\{ {0;12;24;36;48;...} \right\}\)
\(BC(8 ;12) = \left\{ {0;24;48;...} \right\}\)