\(a,\dfrac{9}{7}-\left[\dfrac{1}{2}-\left(-\dfrac{2}{7}-\dfrac{1}{10}\right)\right]\)
\(=\dfrac{9}{7}-\left[\dfrac{1}{2}+\dfrac{2}{7}+\dfrac{1}{10}\right]\)
\(=\dfrac{9}{7}-\dfrac{1}{2}-\dfrac{2}{7}-\dfrac{1}{10}\)
\(=\left(\dfrac{9}{7}-\dfrac{2}{7}\right)-\left(\dfrac{1}{2}+\dfrac{1}{10}\right)\)
\(=1-\left(\dfrac{5}{10}+\dfrac{1}{10}\right)\)
\(=\dfrac{10}{10}-\dfrac{6}{10}\)
\(=\dfrac{4}{10}=\dfrac{2}{5}\)
\(b,\dfrac{5}{3}+\left[-\left(\dfrac{7}{12}-\dfrac{2}{3}\right)+\dfrac{1}{3}\right]\)
\(=\dfrac{5}{3}-\dfrac{7}{12}+\dfrac{2}{3}+\dfrac{1}{3}\)
\(=\left(\dfrac{5}{3}+\dfrac{2}{3}+\dfrac{1}{3}\right)-\dfrac{7}{12}\)
\(=\dfrac{8}{3}-\dfrac{7}{12}\)
\(=\dfrac{32}{12}-\dfrac{7}{12}=\dfrac{25}{12}\)
a)9/7 -[1/2-(-2/7 - 1/10)]
= 9/7 -[1/2+ 2/7+ 1/10]
= 9/7 - 1/2 - 2/7 - 1/10
= ( 9/7 - 2/7) - ( 1/2 + 1/10 )
= 1 - 3/5 = 2/5