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Tính:
a) \({\rm{}}{{ – 5} \over {13}}.26\) b) \({\left( {{{ – 2} \over 7}} \right)^2}\)
c) \(\left( {2 – {1 \over 2}} \right).\left( {{{ – 3} \over 4} + {1 \over 2}} \right)\)
Giải
a) \({\rm{}}{{ – 5} \over {13}}.26 = {{ – 5.26} \over {13}} = – 10\)
b) \({\left( {{{ – 2} \over 7}} \right)^2} = {{ – 2} \over 7}.{{ – 2} \over 7} = {{\left( { – 2} \right).\left( { – 2} \right)} \over {7.7}} = {4 \over {49}}\)
c) \(\left( {2 – {1 \over 2}} \right).\left( {{{ – 3} \over 4} + {1 \over 2}} \right) \)
\(= \left( {{4 \over 2} – {1 \over 2}} \right).\left( {{{ – 3} \over 4} + {1 \over 2}} \right) \)
\(= {3 \over 2}.{{ – 1} \over 4} = {{3.( – 1)} \over {2.4}} = {{ – 3} \over 8}\)