Tính: a) $\frac{-5}{12}$ . $\frac{4}{19}$ + $\frac{7}{12}$ . $\frac{-4}{19}$ + $\frac{4}{19}$ - $\frac{40}{19}$ b) $\frac{6}{13}$ . $\frac{5}{18}$ + $\frac{-7}{24}$ + $\frac{5}{18}$ . $\frac{7}{13}$ + $\frac{-5}{24}$ c) ( $\frac{4}{5}$ + $\frac{2}{3}$ ) : $\frac{1}{5}$ - 1,4 . $(\frac{-5}{7})^{2}$

Đáp án+Giải thích các bước giải:

`a. {-5}/{12} . 4/{19} + 7/{12} . {-4}/{19} + 4/{19}-{40}/{19}`

`={-4}/{19}(5/{12}+7/{12}-1)-{40}/{19}`

`={-4}/{19}({5+7-12}/{12})-{40}/{19}`

`={-4}/{19}.0-{40}/{19}`

`=0-{40}/{19}`

`={-40}/{19}`

`b. 6/{13}.5/{18}+{-7}/{24}+5/{18}.7/{13}+{-5}/{24}`

`=5/{18}(6/{13}+7/{13})+({-7}/{24}-5/{24})`

`=5/{18}({6+7}/{13})+({-7-5}/{24})`

`=5/{18}.1+{-12}/{24}`

`=5/{18}-1/{2}`

`={5-9}/{18}`

`={-4}/{18}`

`={-2}/9`

`c. (4/5+2/3):1/5-1,4.({-5}/{7})^2`

`={12+10}/{15}:1/5-7/5.{25}/{49}`

`={22}/{15}.5-5/7`

`={22}/3-5/7`

`={154-15}/{21}`

`={139}/{21}`

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@Changg_Aquatic World