Tìm x, biết a) (x - 2/5) : 2/3 = 3/4 b) (x + -3/4) - 1/2 = 2/3 . 3/5

* Hướng dẫn giải

$\begin{array}{l}a)\left(x-\frac{2}{5}\right)\text{:}\frac{2}{3}\text{=}\frac{3}{4}\\ x-\frac{2}{5}=\frac{3}{4}.\frac{2}{3}\\ x-\frac{2}{5}=\frac{1}{2}\\ x=\frac{9}{10}\end{array}$

$\begin{array}{l}b)\left(x+\frac{-3}{4}\right)-\frac{1}{2}=\frac{2}{3}\text{.}\frac{3}{5}\\ \left(x+\frac{-3}{4}\right)-\frac{1}{2}=\frac{2}{5}\\ x+\frac{-3}{4}=\frac{9}{10}\\ x=\frac{33}{20}\end{array}$

$\begin{array}{l}c)\left|x-\frac{2}{7}\right|\text{=}\frac{-9}{14}\text{.}\frac{-4}{3}\\ \left|x-\frac{2}{7}\right|\text{=}\frac{6}{7}\\ \text{+) }x-\frac{2}{7}\text{=}\frac{6}{7}\\ x=\frac{8}{7}\\ \text{+) }x-\frac{2}{7}\text{=}\frac{-6}{7}\\ x=\frac{-4}{7}\end{array}$