Đáp án + Giải thích các bước giải:

1) $\dfrac{- 9}{7}$ . ( $\dfrac{a}{b}$ + $\dfrac{a}{b}$)

= $\dfrac{- 9}{7}$ . $\dfrac{77}{45}$

= - $\dfrac{11}{5}$

2) ( $\dfrac{2}{3}$ - $\dfrac{6}{5}$) . $\dfrac{15}{- 36}$

= - $\dfrac{8}{15}$ . $\dfrac{15}{- 36}$

= $\dfrac{2}{9}$

3) ( $\dfrac{3}{29}$ - $\dfrac{1}{5}$) . $\dfrac{29}{3}$

= - $\dfrac{14}{145}$ . $\dfrac{29}{3}$

= - $\dfrac{14}{15}$

4) $\dfrac{5}{7}$ . ( $\dfrac{3}{5}$ + $\dfrac{7}{2}$)

= $\dfrac{5}{7}$ . $\dfrac{41}{10}$

= $\dfrac{41}{14}$

5) $\dfrac{- 8}{11}$ . ( $\dfrac{33}{24}$ - $\dfrac{11}{16}$)

= $\dfrac{- 8}{11}$ . $\dfrac{11}{16}$

= - $\dfrac{1}{2}$

6) $\dfrac{6}{7}$ . ( $\dfrac{- 5}{3}$ + $\dfrac{7}{- 5}$)

= $\dfrac{6}{7}$ . ( - $\dfrac{46}{15}$)

= - $\dfrac{92}{35}$

7) $\dfrac{20}{9}$ . ( - $\dfrac{27}{10}$ + $\dfrac{3}{5}$)

= $\dfrac{20}{9}$ . ( - $\dfrac{21}{10}$)

= - $\dfrac{14}{3}$

8) $\dfrac{- 1}{36}$ . ( $\dfrac{9}{2}$ + $\dfrac{18}{7}$)

= $\dfrac{- 1}{36}$ . $\dfrac{99}{14}$

= - $\dfrac{11}{56}$

9) ( $\dfrac{- 7}{4}$ - $\dfrac{5}{3}$) . $\dfrac{6}{35}$

= - $\dfrac{41}{12}$ . $\dfrac{6}{35}$

= - $\dfrac{41}{70}$

10) ( $\dfrac{10}{21}$ - $\dfrac{5}{28}$) . $\dfrac{7}{30}$

= $\dfrac{25}{84}$ . $\dfrac{7}{30}$

= $\dfrac{5}{72}$

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