Tìm \(x\), biếta. \(\dfrac{2}{3} + \dfrac{7}{4}:x...

A

- Hướng dẫn giải

Phương pháp giải:

Giải chi tiết:

\(\begin{array}{l}a)\dfrac{2}{3} + \dfrac{7}{4}:x = \dfrac{5}{6}\\\dfrac{7}{4}:x = \dfrac{5}{6} - \dfrac{2}{3}\\\dfrac{7}{4}:x = \dfrac{5}{6} - \dfrac{4}{6}\\\dfrac{7}{4}:x = \dfrac{1}{6}\\x = \dfrac{7}{4}:\dfrac{1}{6}\\x = \dfrac{{21}}{2}\end{array}\)

\(\begin{array}{l}b)\dfrac{3}{2} - \left( {x - \dfrac{5}{6}} \right) = \dfrac{8}{9}\\x - \dfrac{5}{6} = \dfrac{3}{2} - \dfrac{8}{9}\\x - \dfrac{5}{6} = \dfrac{{27}}{{18}} - \dfrac{{16}}{{18}}\\x - \dfrac{5}{6} = \dfrac{{11}}{{18}}\\x = \dfrac{{11}}{{18}} + \dfrac{5}{6}\\x = \dfrac{{13}}{9}\end{array}\)

c) \(\left( {4x - 9} \right)\left( {2,5 + \dfrac{{ - 7}}{3}x} \right) = 0\)

\( \Rightarrow 4x - 9 = 0\) hoặc \(2,5 + \dfrac{{ - 7}}{3}x = 0\)

+) \(4x - 9 = 0 \Rightarrow x = \dfrac{9}{4}\)

+) \(2,5 + \dfrac{{ - 7}}{3}x = 0 \Rightarrow \dfrac{{ - 7}}{3}x =  - 2,5\)

\(x =  - 2,5:\dfrac{{ - 7}}{3}\)

\(x = \dfrac{{15}}{{14}}\)

Vậy \(x = \dfrac{9}{4}\) hoặc \(x = \dfrac{{15}}{{14}}\)