\[\boxed{\text{446\ (446).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
Пояснение.
Решение.
\[1)\ A = \left\{ 2,\ 7,\ 8 \right\};\ \ B = \{ 3,\ 5,\ 6,\ 8\}\]
\[\ \ A \cup B = \left\{ 2,\ 3,\ 5,\ 6,\ 7,\ 8 \right\};\]
\[2)\ A = \left\{ 5 \right\},;\ B = \{ 7\}\]
\[\ \ A \cup B = \left\{ 5,\ 7 \right\}.\ \]
\[\boxed{\text{446.}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[1)\ x \geq 9\]
\[\lbrack 9; + \infty).\]
\[2) - 7 \leq x \leq 2\]
\[\lbrack - 7;2\rbrack.\]
\[3) - 2,8 < x \leq 1,4\]
\[( - 2,8;1,4\rbrack.\]
\[4)\ x < 1\]
\[( - \infty;\ 1).\]