Thực hiện phép tính:a. \(\dfrac{7}{{23}}.\left[ {\...

A

- Hướng dẫn giải

Phương pháp giải:

Giải chi tiết:

Hướng dẫn giải chi tiết

a. $\dfrac{7}{{23}}.\left[ {\left( { - \dfrac{8}{6}} \right) - \dfrac{{45}}{{18}}} \right]$

$\begin{array}{l} = \dfrac{7}{{23}}\left[ {\dfrac{{ - 4}}{3} - \dfrac{5}{2}} \right]\\ = \dfrac{7}{{23}}\left( {\dfrac{{ - 8}}{6} - \dfrac{{15}}{6}} \right)\\ = \dfrac{7}{{23}}.\dfrac{{ - 23}}{6}\\ = \dfrac{{ - 7}}{6}\end{array}$

b. $\left( {\dfrac{{ - 2}}{3} + \dfrac{3}{7}} \right):\dfrac{4}{5} + \left( {\dfrac{{ - 1}}{3} + \dfrac{4}{7}} \right):\dfrac{4}{5}$

$\begin{array}{l} = \left( {\dfrac{{ - 2}}{3} + \dfrac{3}{7} + \dfrac{{ - 1}}{3} + \dfrac{4}{7}} \right):\dfrac{4}{5}\\ = \left[ {\left( {\dfrac{{ - 2}}{3} + \dfrac{{ - 1}}{3}} \right) + \left( {\dfrac{3}{7} + \dfrac{4}{7}} \right)} \right]:\dfrac{4}{5}\\ = \left( { - 1 + 1} \right):\dfrac{4}{5}\\ = 0:\dfrac{4}{5}\\ = 0\end{array}$

c. $- \dfrac{8}{3} + \left( {\dfrac{2}{3} - 1 + \dfrac{1}{2}} \right) - \left( { - \dfrac{5}{4} + \dfrac{1}{2}} \right)$

$\begin{array}{l} = - \dfrac{8}{3} + \dfrac{2}{3} - 1 + \dfrac{1}{2} + \dfrac{5}{4} - \dfrac{1}{2}\\ = \left( { - \dfrac{8}{3} + \dfrac{2}{3}} \right) - 1 + \left( {\dfrac{1}{2} - \dfrac{1}{2}} \right) + \dfrac{5}{4}\\ = - 2 - 1 + 0 + \dfrac{5}{4}\\ = - 3 + \dfrac{5}{4}\\ = - \dfrac{7}{4}\end{array}$