\[\boxed{\mathbf{839\ (839)}\mathbf{.}\mathbf{\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[\textbf{а)}\ a = - 8,\ \ \ b = - 1:\]
\[2ab = 2 \cdot ( - 8) \cdot ( - 1) = - 16 \cdot ( - 1) = 16 \cdot 1 = 16.\]
\[\textbf{б)}\ a = 10,\ \ \ b = - 2:\]
\[8 - (a + b) = 8 - \left( ( - 10) + ( - 2) \right) = 8 - ( - 12) = 8 + 12 = 20.\]
\[Ответ:\ \ а)\ 16;\ \ \ б)\ 20.\]