\[\boxed{\mathbf{796\ (796)}\mathbf{.}\mathbf{\ }Еуроки\ - \ ДЗ\ без\ мороки}\]
\[1)\ a = 16;\ \ b = - 12:\]
\[a \bullet b = 16 \bullet ( - 12) = - 192.\]
\[2) - ab = - \left( \text{ab} \right) = 192\]
\[a \bullet ( - b) = - \left( \text{ab} \right) = 192\]
\[( - a) \bullet ( - b) = ab = - 192\]
\[- ( - a) \bullet b = ab = - 192\]
\[- ( - a) \bullet ( - b) = a \bullet ( - b) = - ab = 192\]
\[3)\ ab = - ab = ( - a) \bullet ( - b) = - ( - a) \bullet b.\]