Thực hiện các phép tính :
a) \({{ - 4} \over 5}.{{15} \over {16}}\) b) \({{ - 5} \over 6}.{{ - 3} \over {10}}\)
c) \({{ - 4} \over {27}}:{2 \over { - 9}}\) d) \({7 \over 6}:{{14} \over { - 9}}\)
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e) \( - 18:{3 \over 5}\) f) \({3 \over 8}:\left( { - 9} \right)\).
\(\eqalign{ & a){{ - 4} \over 5}.{{15} \over {16}} = {{( - 4).15} \over {5.16}} = {{( - 1).3} \over {1.4}} = {{ - 3} \over 4} \cr & b){{ - 5} \over 6}.{{ - 3} \over {10}} = {{( - 5).( - 3)} \over {6.10}} = {{( - 1).( - 1)} \over {2.2}} = {1 \over 4} \cr & c){{ - 4} \over {27}}:{2 \over { - 9}} = {{ - 4} \over {27}}.{{ - 9} \over 2} = {{( - 4).( - 9)} \over {27.2}} = {{( - 2).( - 1)} \over {1.3}} = {2 \over 3} \cr & d){7 \over 6}:{{14} \over { - 9}} = {7 \over 6}.{{ - 9} \over {14}} = {{7.( - 9)} \over {6.14}} = {{1.( - 3)} \over {2.2}} = {{ - 3} \over 4} \cr & e) - 18:{3 \over 5} = - 18.{5 \over 3} = {{( - 18).5} \over 3} = {{( - 6).5} \over 1} = - 30 \cr & f){3 \over 8}:( - 9) = {3 \over {8.( - 9)}} = {1 \over {8.( - 3)}} = {{ - 1} \over {24}} \cr} \)