Bài 1:
\(a,\dfrac{2}{3}-4\left(\dfrac{1}{2}+\dfrac{3}{4}\right)\)
\(=\dfrac{2}{3}-4\left(\dfrac{2}{4}+\dfrac{3}{4}\right)\)
\(=\dfrac{2}{3}-4.\dfrac{5}{4}\)
\(=\dfrac{2}{3}-5\)
\(=\dfrac{2}{3}-\dfrac{15}{3}\)
\(=\dfrac{-13}{3}\)
\(b,\left(\dfrac{-1}{3}+\dfrac{5}{6}\right).11-7\)
\(=\left(\dfrac{-2}{6}+\dfrac{5}{6}\right).11-7\)
\(=\dfrac{3}{6}.11-7\)
\(=\dfrac{1}{2}.11-7\)
\(=\dfrac{11}{2}-7\)
\(=\dfrac{11}{2}-\dfrac{14}{2}\)
\(=\dfrac{-3}{2}\)
\(c,\dfrac{-1}{24}-\left[\dfrac{1}{4}-\left(\dfrac{1}{2}-\dfrac{7}{8}\right)\right]\)
\(=\dfrac{-1}{24}-\left[\dfrac{1}{4}-\left(\dfrac{4}{8}-\dfrac{7}{8}\right)\right]\)
\(=\dfrac{-1}{24}-\left[\dfrac{1}{4}-\dfrac{-3}{8}\right]\)
\(=\dfrac{-1}{24}-\left[\dfrac{2}{8}+\dfrac{3}{8}\right]\)
\(=\dfrac{-1}{24}-\dfrac{5}{8}\)
\(=\dfrac{-1}{24}-\dfrac{15}{24}\)
\(=\dfrac{-16}{24}=\dfrac{-2}{3}\)
\(d,\left(\dfrac{5}{7}-\dfrac{7}{5}\right)-\left[\dfrac{1}{2}-\left(-\dfrac{2}{7}-\dfrac{1}{10}\right)\right]\)
\(=\left(\dfrac{25}{35}-\dfrac{49}{35}\right)-\left[\dfrac{1}{2}-\left(-\dfrac{20}{70}-\dfrac{7}{70}\right)\right]\)
\(=\dfrac{-24}{35}-\left[\dfrac{1}{2}-\dfrac{-27}{70}\right]\)
\(=\dfrac{-24}{35}-\left[\dfrac{35}{70}+\dfrac{27}{70}\right]\)
\(=\dfrac{-24}{35}-\dfrac{62}{70}\)
\(=\dfrac{-24}{35}-\dfrac{31}{35}\)
\(=\dfrac{-55}{35}=\dfrac{-11}{7}\)
Bài 2:
\(a,x\left(-\dfrac{3}{7}\right)=\dfrac{5}{21}\)
\(x=\dfrac{5}{21}:\dfrac{-3}{7}\)
\(x=\dfrac{5}{21}.\dfrac{-7}{3}\)
\(x=\dfrac{5.\left(-1\right)}{3.3}\)
\(x=\dfrac{-5}{9}\)
\(b,1\dfrac{5}{9}x=\dfrac{28}{9}\)
\(\dfrac{14}{9}x=\dfrac{28}{9}\)
\(x=\dfrac{28}{9}:\dfrac{14}{9}\)
\(x=\dfrac{28}{9}.\dfrac{9}{14}\)
\(x=\dfrac{2.1}{1.1}\)
\(x=2\)
\(c,x:\left(-\dfrac{2}{5}\right)=-\dfrac{15}{16}\)
\(x=\dfrac{-15}{16}.\dfrac{-2}{5}\)
\(x=\dfrac{\left(-3\right).\left(-1\right)}{8.1}\)
\(x=\dfrac{3}{8}\)
\(d,\dfrac{-4}{7}:x=-\dfrac{2}{5}\)
\(x=\dfrac{-4}{7}:\dfrac{-2}{5}\)
\(x=\dfrac{-4}{7}.\dfrac{-5}{2}\)
\(x=\dfrac{\left(-2\right).\left(-5\right)}{7}\)
\(x=\dfrac{10}{7}\)
( Lần sau bn chú ý tách nhỏ bài ra cho dễ làm nhé :33)