\[\boxed{\text{472.}\text{\ }\text{еуроки}\text{-}\text{ответы}\text{\ }\text{на}\text{\ }\text{пятёрку}}\]
\[a < 0,\ \ b < 0:\]
\[- a > 0;\ - b > 0.\]
\[\textbf{а)}\ \sqrt{\text{ab}} = \sqrt{- a} \cdot \sqrt{- b}\]
\[\textbf{б)}\ \sqrt{\frac{a}{b}} = \frac{\sqrt{- a}}{\sqrt{- b}}\ \]