Tìm x a) 3x/13 = 45/-26 . -2/5 b) (13/21 - 3/2) . 21/13 + x = 4/13

* Hướng dẫn giải

a)

$\begin{array}{l}\frac{3.x}{13}=\frac{45}{-26}.\frac{-2}{5}\\ \frac{3.x}{13}=\frac{9}{13}\\ 3.x=9\\ x=3\end{array}$

b)

$\begin{array}{l}\left(\frac{13}{21}-\frac{3}{2}\right).\frac{21}{13}+x=\frac{4}{13}\\ \frac{-27}{42}.\frac{21}{13}+x=\frac{4}{13}\\ \frac{-27}{26}+x=\frac{4}{13}\\ x=\frac{4}{13}-\frac{-27}{26}\\ x=\frac{35}{26}\end{array}$