a, $\dfrac{-3}{7}+\dfrac{15}{26}-(\dfrac{2}{13}-\dfrac{3}{7})$
$=\dfrac{-3}{7}+\dfrac{15}{26}-\dfrac{2}{13}+\dfrac{3}{7}$
$=\dfrac{-3}{7}+\dfrac{3}{7}+\dfrac{15}{26}-\dfrac{2}{13}$
$=\dfrac{15}{26}-\dfrac{4}{26}$
$=\dfrac{11}{26}$
b, $2\dfrac{23}{7}+(\dfrac{2}{9}-1\dfrac{3}{7})-\dfrac{-5}{3}:\dfrac{1}{9}$ (dấu = mình thay bằng dấu +)
$=\dfrac{37}{7}+\dfrac{2}{9}-\dfrac{10}{7}+\dfrac{5}{3}\cdot9$
$=\dfrac{37}{7}-\dfrac{10}{7}+\dfrac{2}{9}+15$
$=\dfrac{27}{7}+\dfrac{137}{9}$
$=\dfrac{1202}{63}$
