Tìm x, biết:
a) \(x.{3 \over 7} = {2 \over 3}\) d) \({4 \over 7}.x - {2 \over 3} = {1 \over 5}\)
b) \(x:{8 \over {11}} = {{11} \over 3}\) e) \({2 \over 9} - {7 \over 8}.x = {1 \over 3}\)
c) \({2 \over 5}:x = {{ - 1} \over 4}\) g) \({4 \over 5} + {5 \over 7}:x = {1 \over 6}\)
a)Từ \(x.{3 \over 7} = {2 \over 3}\) suy ra \(x = {2 \over 3}:{3 \over 7} = {2 \over 3}.{7 \over 3} = {{14} \over 9}\)
b)Từ \(x:{8 \over {11}} = {{11} \over 3}\) suy ra \(x = {{11} \over 3}.{8 \over {11}} = {8 \over 3}\)
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c)Từ \({2 \over 5}:x = {{ - 1} \over 4}\) suy ra \(x = {2 \over 5}:{{ - 1} \over 4} = {2 \over 5}.{4 \over { - 1}} = {8 \over { - 5}} = {{ - 8} \over 5}\)
d)Từ \({4 \over 7}.x - {2 \over 3} = {1 \over 5}\) suy ra \({4 \over 7}.x = {1 \over 5} + {2 \over 3} = {{3 + 10} \over {15}} = {{13} \over {15}}\)
Do đó: \(x = {{13} \over {15}}:{4 \over 7} = {{13} \over {15}}.{7 \over 4} = {{91} \over {60}}\) .
e)Từ \({2 \over 9} - {7 \over 8}.x = {1 \over 3}\) suy ra \({2 \over 9} - {1 \over 3} = {7 \over 8}.x\) hay \({7 \over 8}x = {{2 - 3} \over 9} = {{ - 1} \over 9}\)
Do đó \(x = {{ - 1} \over 9}:{7 \over 8} = {{ - 1} \over 9}.{8 \over 7} = {{ - 8} \over {63}}\)
g)Từ \({4 \over 5} + {5 \over 7}:x = {1 \over 6}\) Suy ra \({5 \over 7}:x = {1 \over 6} - {4 \over 5} = {{5 - 24} \over {30}} = {{ - 19} \over {30}}\)
Do đó: \(x = {5 \over 7}:{{ - 19} \over {30}} = {{5.30} \over {7.\left( { - 19} \right)}} = {{150} \over { - 133}} = {{ - 150} \over {133}}\)