Tròiiii oiiii đừngggg chê ít đỉm nhaaaa cầu xin mn giúp tooiiiii

$\dfrac{3+  \dfrac{3}{13} + \dfrac{3}{169} + \dfrac{3}{91} }{7 + \dfrac{7}{13} + \dfrac{7}{169} + \dfrac{7}{91} }$

$ = \dfrac{3 (\dfrac{1}{13} + \dfrac{1}{169} + \dfrac{1}{91}) }{7 (\dfrac{1}{13} + \dfrac{1}{169} + \dfrac{1}{91}) }$

$ = \dfrac{3}{7}$

---

Sửa lại đề bài: 

$\dfrac{ ( \dfrac{-5}{7} - \dfrac{7}{9} + \dfrac{9}{11}) . (3 - \dfrac{3}{4}) }{ ( \dfrac{10}{21} + \dfrac{14}{27} - \dfrac{18}{33}) : (2 - \dfrac{2}{3}) }$

$ = \dfrac{ ( \dfrac{-5}{7} - \dfrac{7}{9} + \dfrac{9}{11}) . (\dfrac{12}{4} - \dfrac{3}{4}) }{ \dfrac{-2}{3}  ( \dfrac{-5}{7} - \dfrac{7}{9} + \dfrac{9}{11}) : (\dfrac{6}{3}- \dfrac{2}{3}) }$

$ = \dfrac{ ( \dfrac{-5}{7} - \dfrac{7}{9} + \dfrac{9}{11}) . \dfrac{9}{4}}{ \dfrac{-2}{3} ( \dfrac{-5}{7} - \dfrac{7}{9} + \dfrac{9}{11}) : \dfrac{4}{3}}$

$ = \dfrac{ ( \dfrac{-5}{7} - \dfrac{7}{9} + \dfrac{9}{11}) . 3 . \dfrac{3}{4}}{ \dfrac{-2}{3} ( \dfrac{-5}{7} - \dfrac{7}{9} + \dfrac{9}{11}) . \dfrac{3}{4}}$

$ = \dfrac{3}{\dfrac{-2}{3}}$

` = -9/2`