1. Làm các phép tính :
a) \({5 \over 6}:{{ - 10} \over 3}\)
b) \( - {7 \over {12}}:{{ - 21} \over 8}\)
c) \( - 7:{7 \over 6}\)
d) \({{ - 7} \over 6}:\left( { - 14} \right)\)
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2. Tìm x, biết :
a) \({5 \over 7}.x = {5 \over 6}\)
b) \({4 \over 5}:x = {2 \over 3}\).
\(\eqalign{ & 1.a){5 \over 6}:{{ - 10} \over 3} = {5 \over 6}.{3 \over { - 10}} = {{15} \over { - 60}} = {{ - 1} \over 4} \cr & b) - {7 \over {12}}:{{ - 21} \over 8} = {{ - 7} \over {12}}.{8 \over { - 21}} = {2 \over 9} \cr & c) - 7:{7 \over 6} = - 7.{6 \over 7} = - 6 \cr & d){{ - 7} \over 6}:( - 14) = {{ - 7} \over {6.( - 14)}} = {1 \over {12}} \cr & 2.a){5 \over 7}.x = {5 \over 6} \cr & x = {5 \over 6}:{5 \over 7} \cr & x = {5 \over 6}.{7 \over 5} \Leftrightarrow x = {7 \over 6} \cr & b){4 \over 5}:x = {2 \over 3} \cr & x = {4 \over 5}:{2 \over 3} \cr & x = {4 \over 5}.{3 \over 2} \Leftrightarrow x = {6 \over 5}. \cr} \)