\(a)\dfrac{4}{5}-\left(\dfrac{-2}{7}\right)-\dfrac{7}{10}\)
\(=\dfrac{56}{70}+\dfrac{20}{70}+\dfrac{-49}{70}\)
\(=\dfrac{27}{70}\)
\(b)\left(6-\dfrac{2}{3}+\dfrac{1}{2}\right)-\left(5+\dfrac{5}{3}-\dfrac{3}{2}\right)-\left(3-\dfrac{7}{3}+\dfrac{5}{2}\right)\)
\(=\left(\dfrac{36}{6}+\dfrac{-4}{6}+\dfrac{3}{6}\right)-\left(\dfrac{30}{6}+\dfrac{10}{6}+\dfrac{-9}{6}\right)-\left(\dfrac{18}{6}+\dfrac{-14}{6}+\dfrac{15}{6}\right)\)
\(=\dfrac{35}{6}-\dfrac{31}{6}-\dfrac{19}{6}\)
\(=\dfrac{35+\left(-31\right)+\left(-19\right)}{6}\)
\(=-\dfrac{15}{6}=-2\dfrac{1}{2}\)
\(\dfrac{4}{5}-\left(-\dfrac{2}{7}\right)-\dfrac{7}{10}=\dfrac{4}{5}+\dfrac{2}{7}+\dfrac{-7}{10}=\dfrac{56}{70}+\dfrac{20}{70}+\dfrac{-49}{70}=\dfrac{-27}{70}\)
\(\left(6-\dfrac{2}{3}+\dfrac{1}{2}\right)-\left(5+\dfrac{5}{3}-\dfrac{3}{2}\right)-\left(3-\dfrac{7}{3}+\dfrac{5}{2}\right)\)
= \(6-\dfrac{2}{3}+\dfrac{1}{2}-5-\dfrac{5}{3}+\dfrac{3}{2}-3+\dfrac{7}{3}-\dfrac{5}{2}\)
= \(\left(6-5-3\right)+\left(\dfrac{-2}{3}+\dfrac{-5}{3}+\dfrac{7}{3}\right)+\left(\dfrac{1}{2}+\dfrac{3}{2}-\dfrac{5}{2}\right)\)
=\(\left(-2\right)+0+\left(\dfrac{-1}{2}\right)\)
=\(\dfrac{-2}{1}+\dfrac{-1}{2}=\dfrac{\left(-4\right)+\left(-1\right)}{2}=\dfrac{-5}{2}\)
a)\(\dfrac{4}{5}\)-\(\left(\dfrac{-2}{7}\right)\)-\(\dfrac{7}{10}\)
=\(\dfrac{56}{70}\)-\(\dfrac{-20}{70}\)-\(\dfrac{49}{70}\)
=\(\dfrac{76}{70}\)-\(\dfrac{49}{70}\)
=\(\dfrac{27}{70}\)