\(a,\dfrac{-4}{5}+\dfrac{2}{7}-\dfrac{1}{5}-\dfrac{9}{7}=\left(\dfrac{-4}{5}-\dfrac{1}{5}\right)+\left(\dfrac{2}{7}-\dfrac{9}{7}\right)=-1+\left(-1\right)=-2\)
\(b,\dfrac{1}{12}-\left(\dfrac{1}{2}+\dfrac{7}{12}\right)=\dfrac{1}{12}-\left(\dfrac{6}{12}+\dfrac{7}{12}\right)=\dfrac{1}{12}-\dfrac{13}{12}=\dfrac{-12}{12}=-1\)
\(c,\dfrac{-12}{5}-\left(\dfrac{3}{5}-\dfrac{1}{8}\right)=\dfrac{-12}{5}-\left(\dfrac{24}{40}-\dfrac{5}{40}\right)=\dfrac{-12}{5}-\dfrac{19}{40}=\dfrac{-96}{40}-\dfrac{16}{40}=\dfrac{-100}{40}=\dfrac{-5}{2}\)
\(d,\dfrac{-5}{7}-\left(\dfrac{-7}{6}+\dfrac{2}{7}\right)+\dfrac{7}{-6}=\dfrac{-5}{7}+\dfrac{7}{6}-\dfrac{2}{7}+\dfrac{-7}{6}=\left(\dfrac{-5}{7}-\dfrac{2}{7}\right)+\left(\dfrac{7}{6}+\dfrac{-7}{6}\right)=-1\)
\(e,\dfrac{-6}{5}-\dfrac{2}{7}+\dfrac{1}{5}-\dfrac{5}{7}=\left(\dfrac{-6}{5}+\dfrac{1}{5}\right)+\left(\dfrac{-2}{7}-\dfrac{5}{7}\right)=-1+\left(-1\right)=-2\)
\(a,-\dfrac{4}{5}+\dfrac{2}{7}-\dfrac{1}{5}-\dfrac{9}{7}\)
\(=\dfrac{2}{7}-\dfrac{9}{7}-\dfrac{4}{5}-\dfrac{1}{5}\)
\(=-\dfrac{7}{7}-\dfrac{5}{5}\)
\(=-1-1=-2\)
\(b,\dfrac{1}{12}-\left(\dfrac{1}{2}+\dfrac{7}{12}\right)\)
\(=\dfrac{1}{12}-\dfrac{7}{12}-\dfrac{1}{2}\)
\(=-\dfrac{6}{12}-\dfrac{1}{2}=-1\)
\(c,-\dfrac{12}{5}-\left(\dfrac{3}{5}-\dfrac{1}{8}\right)\)
\(=-\dfrac{12}{5}-\dfrac{3}{5}+\dfrac{1}{8}\)
\(=-\dfrac{15}{5}+\dfrac{1}{8}\)
\(=-3+\dfrac{1}{8}=-\dfrac{23}{8}\)
\(d,-\dfrac{5}{7}-\left(-\dfrac{7}{6}+\dfrac{2}{7}\right)+\dfrac{7}{-6}\)
=\(-\dfrac{5}{7}+\dfrac{7}{6}-\dfrac{2}{7}-\dfrac{7}{6}\)
\(=-\dfrac{5}{7}-\dfrac{2}{7}\)
\(=-\dfrac{7}{7}=-1\)
\(e.-\dfrac{6}{5}-\dfrac{2}{7}+\dfrac{1}{5}-\dfrac{5}{7}\)
\(=-\dfrac{6}{5}+\dfrac{1}{5}-\dfrac{2}{7}-\dfrac{5}{7}\)
\(=\dfrac{5}{5}-\dfrac{7}{7}\)
\(=1-1=0\)
