Tìm x biết a) x -1/2 = 2/9 + -1/5 b) x/10 = 3/15 -1/2

* Hướng dẫn giải

a) 

$\begin{array}{l}x-\frac{1}{2}=\frac{2}{9}+\frac{-1}{5}\\ x-\frac{1}{2}=\frac{10}{45}+\frac{-9}{45}\\ x-\frac{1}{2}=\frac{1}{45}\\ x=\frac{10}{45}+\frac{1}{2}\\ x=\frac{20}{90}+\frac{45}{90}=\frac{65}{90}=\frac{13}{18}\end{array}$

b)

$\begin{array}{l}\frac{x}{10}=\frac{3}{15}-\frac{1}{2}=\frac{-9}{30}=\frac{-3}{10}\\ x=-3\end{array}$