\[\boxed{\text{870.\ }\text{еуроки}\text{-}\text{ответы}\text{\ }\text{на}\text{\ }\text{пятёрку}}\]
\[a > 0\]
\[\textbf{а)} - a < a\left( \sqrt{3} - \sqrt{2} \right) <\]
\[< a\sqrt{3} < 2a < 3a;\]
\[\textbf{б)}\ 6a > a\left( \sqrt{7} - \sqrt{6} \right) > - a >\]
\[> - a\sqrt{5} > - 5a - 1.\]