\[Страница\ 18.\]
\[5.\ Понятие\ множества\]
\[\boxed{\mathbf{1.}}\]
\[\textbf{д)}\ \left\{ 3;6;9;12;15;18 \right\}.\]
\[\textbf{е)}\ \left\{ A;B;C;D;E;F \right\}.\]
\[\textbf{ж)}\ \left\{ AB;BC;CD;DE;EF;FA \right\}.\]
\[\textbf{з)}\ \left\{ \varnothing \right\}.\]
\[\boxed{\mathbf{2.}}\]
\[\textbf{а)}\ \left\{ 4;3;6;5 \right\}\text{.\ }\]
\[\textbf{б)}\ \left\{ 4;3;6 \right\}.\]
\[\textbf{в)}\ \left\{ 5 \right\}.\]
\[\textbf{г)}\ \left\{ 0;1 \right\}\text{.\ }\]
\[\boxed{\mathbf{3.}}\]
\[A = \left\{ 780;708;870;807 \right\}.\]
\[Множество\ содержит\ \]
\[4\ элемента.\]