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\(\dfrac{3}{4}\cdot\dfrac{2}{5}-\dfrac{3}{4}\cdot\dfrac{2}{7}\)
= \(\dfrac{3}{4}\cdot\left(\dfrac{2}{5}-\dfrac{2}{7}\right)\)
= \(\dfrac{3}{4}\cdot\left(\dfrac{14}{35}-\dfrac{10}{35}\right)\)
= \(\dfrac{3}{4}\cdot\dfrac{4}{35}\)
= \(\dfrac{3}{35}\)
\(4-\frac{5}{12}\times\frac{9}{10}\)
\(=4-\frac{1}{2}\)
\(=\frac{7}{2}\)
~HT~
\(4-\frac{5}{12}\times\frac{9}{10}\rightarrow4-\frac{3}{8}\rightarrow\frac{32}{8}-\frac{2}{8}=\frac{30}{8}=\frac{15}{4}\)
\(\dfrac{3}{4}.\dfrac{2}{3}-\dfrac{1}{6}.\dfrac{3}{4}-\dfrac{3}{4}.\dfrac{1}{2}\)
= \(\dfrac{3}{4}.\left(\dfrac{2}{3}-\dfrac{1}{6}-\dfrac{1}{2}\right)\)
= \(\dfrac{3}{4}.0\)
= 0
\(\dfrac{3}{4}\cdot\dfrac{2}{3}-\dfrac{1}{6}\cdot\dfrac{3}{4}-\dfrac{3}{4}\cdot\dfrac{1}{2}\)
\(=\dfrac{3}{4}\left(\dfrac{2}{3}-\dfrac{1}{6}-\dfrac{1}{2}\right)\)
\(=\dfrac{3}{4}\cdot\left(\dfrac{4}{6}-\dfrac{1}{6}-\dfrac{3}{6}\right)\)
=0
\(a,\dfrac{4}{15}:\dfrac{4}{7}< x< \dfrac{2}{5}\times\dfrac{10}{3}\\ \Leftrightarrow\dfrac{7}{15}< x< \dfrac{4}{3}\\ \Leftrightarrow x=1\)
\(b,\dfrac{3}{5}\times\dfrac{3}{7}+\dfrac{2}{5}\times\dfrac{4}{7}=\dfrac{9}{35}+\dfrac{8}{35}=\dfrac{17}{35}\)