Tìm x biết a) x + 30% x = -1,3 b) 1/3 x + 2/5 (x -1) = 0 c) 3(x - 1/2)

* Hướng dẫn giải

a) $x+30\%x=-1,3$

$\begin{array}{l}x\left(1+\frac{3}{10}\right)=\frac{-13}{10}\\ \frac{13}{10}x=\frac{-13}{10}\\ x=-1\end{array}$

b) $\frac{1}{3}x+\frac{2}{5}\left(x-1\right)=0$

$\begin{array}{l}\frac{1}{3}x+\frac{2}{5}x-\frac{2}{5}=0\\ \frac{11}{15}x=\frac{2}{5}\\ x=\frac{2}{5}:\frac{11}{15}\\ x=\frac{6}{11}\end{array}$

c) $3\left(x-\frac{1}{2}\right)-5\left(x+\frac{3}{5}\right)=-x+\frac{1}{5}$

$\begin{array}{l}3x-\frac{3}{2}-5x-3=-x+\frac{1}{5}\\ x=\frac{-3}{2}-3-\frac{1}{5}\\ x=\frac{-47}{10}\end{array}$