a: \(\dfrac{2}{5}x+\dfrac{5}{7}=\dfrac{3}{10}\)
=>\(\dfrac{2}{5}x=\dfrac{3}{10}-\dfrac{5}{7}=\dfrac{21}{70}-\dfrac{50}{70}=-\dfrac{29}{70}\)
=>\(x=-\dfrac{29}{70}:\dfrac{2}{5}=-\dfrac{29}{70}\cdot\dfrac{5}{2}=\dfrac{-29}{28}\)
b: \(\dfrac{3}{4}x-\dfrac{1}{2}=\dfrac{3}{7}\)
=>\(\dfrac{3}{4}x=\dfrac{3}{7}+\dfrac{1}{2}=\dfrac{6}{14}+\dfrac{7}{14}=\dfrac{13}{14}\)
=>\(x=\dfrac{13}{14}:\dfrac{3}{4}=\dfrac{13}{14}\cdot\dfrac{4}{3}=\dfrac{13\cdot2}{7\cdot3}=\dfrac{26}{21}\)
c: \(-\dfrac{2}{5}+\dfrac{5}{6}x=-\dfrac{4}{15}\)
=>\(\dfrac{5}{6}x=-\dfrac{4}{15}+\dfrac{2}{5}=\dfrac{2}{15}\)
=>\(x=\dfrac{2}{15}:\dfrac{5}{6}=\dfrac{2}{15}\cdot\dfrac{6}{5}=\dfrac{12}{75}=\dfrac{4}{25}\)
