a) Ta có: \(\dfrac{-1}{24}-\left[\dfrac{1}{4}-\left(\dfrac{1}{2}-\dfrac{7}{8}\right)\right]\)
\(=\dfrac{-1}{24}-\left(\dfrac{1}{4}-\dfrac{1}{2}+\dfrac{7}{8}\right)\)
\(=\dfrac{-1}{24}-\dfrac{1}{4}+\dfrac{1}{2}-\dfrac{7}{8}\)
\(=\dfrac{-1}{24}-\dfrac{6}{24}+\dfrac{12}{24}-\dfrac{21}{24}\)
\(=\dfrac{-16}{24}=\dfrac{-2}{3}\)
b) Ta có: \(\left(\dfrac{5}{7}-\dfrac{7}{5}\right)-\left[\dfrac{1}{2}-\left(\dfrac{-2}{7}-\dfrac{1}{10}\right)\right]\)
\(=\dfrac{25-49}{35}-\left(\dfrac{1}{2}+\dfrac{2}{7}+\dfrac{1}{10}\right)\)
\(=\dfrac{-24}{35}-\dfrac{1}{2}-\dfrac{2}{7}-\dfrac{1}{10}\)
\(=\dfrac{-48}{70}-\dfrac{35}{70}-\dfrac{20}{70}-\dfrac{7}{70}\)
\(=\dfrac{-110}{70}=\dfrac{-11}{7}\)
