Đáp án:
$\begin{array}{l}
1)\\
1)\dfrac{{ - 1}}{5}.\left( {\dfrac{{ - 3}}{7}} \right) = \dfrac{{1.3}}{{5.7}} = \dfrac{3}{{35}}\\
2)\dfrac{5}{{ - 4}}.\left( { - \dfrac{{ - 3}}{2}} \right) = \dfrac{{ - 15}}{8}\\
3)12.\left( {\dfrac{{ - 1}}{4}} \right) = - 3\\
4)\dfrac{{ - 7}}{4}.\left( { - \dfrac{{ - 3}}{8}} \right) = \dfrac{{ - 21}}{{32}}\\
5)\dfrac{{ - 3}}{5}.\left( { - 10} \right) = \dfrac{{30}}{5} = 6\\
6)\dfrac{2}{5}.\left( {\dfrac{{ - 15}}{{62}}} \right) = \dfrac{{ - 3}}{{31}}\\
B2)\\
1)\left( {\dfrac{{ - 3}}{7}} \right).\left( { - \dfrac{{21}}{5}} \right) = \dfrac{9}{5}\\
2)\dfrac{7}{3}.\left( {\dfrac{{ - 9}}{{14}}} \right) = \dfrac{{ - 3}}{2}\\
3)\dfrac{5}{8}.\left( { - \dfrac{{ - 16}}{{15}}} \right) = \dfrac{2}{3}\\
4)\left( { - \dfrac{{ - 14}}{{15}}} \right).\left( { - \dfrac{{25}}{7}} \right) = \dfrac{{ - 10}}{3}\\
5)\left( {\dfrac{{ - 18}}{{19}}} \right).\left( {\dfrac{{ - 38}}{9}} \right) = 4\\
6) - 15.\left( { - \dfrac{7}{{10}}} \right) = \dfrac{{21}}{2}\\
7)\left( {\dfrac{{ - 15}}{9}} \right).8 = \dfrac{{ - 40}}{3}\\
8)\dfrac{{ - 12}}{{13}}.\left( { - 26} \right) = - 24\\
9)14.\left( { - \dfrac{{15}}{{21}}} \right) = - 6\\
10)\left( {\dfrac{{ - 17}}{{25}}} \right).\dfrac{{15}}{{34}} = \dfrac{{ - 3}}{{10}}\\
11)\left( {\dfrac{{ - 21}}{5}} \right).\left| {\dfrac{{ - 10}}{{63}}} \right| = \dfrac{{ - 2}}{3}\\
12)\left| {\dfrac{{ - 12}}{{17}}} \right|.\left( {\dfrac{{ - 34}}{9}} \right) = \dfrac{{ - 4}}{3}
\end{array}$
