tính hợp lí
\(5,-\dfrac{2}{7}-\left(\dfrac{5}{11}-\dfrac{9}{7}\right)+\dfrac{5}{11}=-\dfrac{2}{7}-\dfrac{5}{11}+\dfrac{9}{7}+\dfrac{5}{11}=\left(-\dfrac{2}{7}+\dfrac{9}{7}\right)-\left(\dfrac{5}{11}-\dfrac{5}{11}\right)=1-0=1\\ 6,\dfrac{2}{3}+\dfrac{-2}{5}+\dfrac{-5}{6}-\dfrac{13}{10}=\left(\dfrac{4}{6}+\dfrac{-5}{6}\right)+\left(\dfrac{-4}{10}-\dfrac{13}{10}\right)=\dfrac{-1}{6}+\dfrac{-17}{10}=\dfrac{-5}{30}+\dfrac{-51}{30}=\dfrac{-56}{30}=\dfrac{-28}{15}\)
\(7,\dfrac{-5}{9}+\dfrac{8}{15}+\dfrac{4}{-9}+\dfrac{7}{15}=\left(\dfrac{-5}{9}+\dfrac{-4}{9}\right)+\left(\dfrac{8}{15}+\dfrac{7}{15}\right)=\left(-1\right)+1=0\\ 8,\left(\dfrac{12}{13}+7\right)-\left(-\dfrac{1}{13}+8\right)=\dfrac{12}{13}+7+\dfrac{1}{13}-8=\left(\dfrac{12}{13}+\dfrac{1}{13}\right)+\left(7-8\right)=1+\left(-1\right)=0\)
