Dạng : Tính nhanh [2]e. \(\frac{-3}{5}\). \(\frac{5}{7}\) + \(\frac{-3}{5}\). \(\frac{3}{7}\)+ \(\frac{-3}{5}\). \(\frac{6}{7}\)f. \(\frac{1}{3}\). \(\frac{4}{5}\)+ \(\frac{1}{3}\). \(\frac{6}{5}\)- \(\frac{4}{5}\)g. \(\frac{4}{19}\). \(\frac{-3}{7}\)+ \(\frac{-3}{7}\). \(\frac{15}{19}\)+ \(\frac{5}{7}\)h . \(\frac{5}{9}\). \(\frac{7}{13}\)+ \(\frac{5}{9}\). \(\frac{9}{13}\) - \(\frac{5}{9}\). \(\frac{3}{13}\)i. [\(\frac{-4}{5}\)+ \(\frac{4}{3}\)] +...
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Dạng : Tính nhanh [2]
e. \(\frac{-3}{5}\). \(\frac{5}{7}\) + \(\frac{-3}{5}\). \(\frac{3}{7}\)+ \(\frac{-3}{5}\). \(\frac{6}{7}\)
f. \(\frac{1}{3}\). \(\frac{4}{5}\)+ \(\frac{1}{3}\). \(\frac{6}{5}\)- \(\frac{4}{5}\)
g. \(\frac{4}{19}\). \(\frac{-3}{7}\)+ \(\frac{-3}{7}\). \(\frac{15}{19}\)+ \(\frac{5}{7}\)
h . \(\frac{5}{9}\). \(\frac{7}{13}\)+ \(\frac{5}{9}\). \(\frac{9}{13}\) - \(\frac{5}{9}\). \(\frac{3}{13}\)
i. [\(\frac{-4}{5}\)+ \(\frac{4}{3}\)] + [ \(\frac{-5}{4}\) + \(\frac{14}{5}\)]
e. \(\frac{-3}{5}\cdot\frac{5}{7}+\frac{-3}{5}\cdot\frac{3}{7}+\frac{-3}{5}\cdot\frac{6}{7}=-\frac{3}{5}\left(\frac{5}{7}+\frac{3}{7}+\frac{6}{7}\right)=-\frac{3}{5}\cdot2=-\frac{6}{5}\)
f. \(\frac{1}{3}\cdot\frac{4}{5}+\frac{1}{3}\cdot\frac{6}{5}-\frac{4}{5}=\frac{1}{3}\left(\frac{4}{5}+\frac{6}{5}\right)-\frac{4}{5}=\frac{1}{3}\cdot2-\frac{4}{5}=\frac{2}{3}-\frac{4}{5}=-\frac{2}{15}\)
g. \(\frac{4}{19}\cdot\frac{-3}{7}+\frac{-3}{7}\cdot\frac{15}{19}+\frac{5}{7}=-\frac{3}{7}\left(\frac{4}{19}+\frac{15}{19}\right)+\frac{5}{7}=-\frac{3}{7}\cdot1+\frac{5}{7}=-\frac{3}{7}+\frac{5}{7}=\frac{2}{7}\)
h. \(\frac{5}{9}\cdot\frac{7}{13}+\frac{5}{9}\cdot\frac{9}{13}-\frac{5}{9}\cdot\frac{3}{13}=\frac{5}{9}\left(\frac{7}{13}+\frac{9}{13}-\frac{3}{13}\right)=\frac{5}{9}\cdot1=\frac{5}{9}\)