Tính
a) \({{ - 3} \over 5}.{{15} \over { - 7}}.{{21} \over 6}\)
b) \({{ - 33} \over {25}}.{{15} \over {11}}.{{21} \over 6}\)
c) \({{ - 22} \over {25}}:{{11} \over 5}.{{21} \over 6}\)
d) \({{ - 3} \over 5}.\left[ {\left( { - {{15} \over {11}}} \right) - {{21} \over {33}}} \right]\)
\(\eqalign{ & a){{ - 3} \over 5}.{{15} \over { - 7}}.{{21} \over 6} = - 3.{3 \over { - 7}}.{7 \over 2} = {9 \over 2} = 4{1 \over 2} \cr & b){{ - 33} \over {25}}.{{15} \over {11}}.{{21} \over {16}} = {{ - 3} \over 5}.{3 \over 1}.{{21} \over {16}} = {{ - 189} \over {80}} = - 2{{29} \over {80}} \cr & c){{ - 22} \over {25}}:{{11} \over 5}.{{21} \over {16}} = {{ - 22} \over {25}}.{5 \over {11}}.{{21} \over {16}} = {{ - 2} \over 5}.1.{{21} \over {16}} = {{ - 21} \over {40}} \cr & d){{ - 3} \over 5}.\left[ {\left( { - {{15} \over {11}}} \right) - {{21} \over {33}}} \right] = {{ - 3} \over 5}.\left( {{{ - 45 - 21} \over {33}}} \right) = {{ - 3} \over 5}.\left( { - {{66} \over {33}}} \right) = {6 \over 5} = 1{1 \over 5} \cr} \)