Tìm x biết a) x + 1/5 = -4/9 b) 5/7 - x = - 9/21

* Hướng dẫn giải

a) $x+\frac{1}{5}=\frac{-4}{9}$

$\begin{array}{l}x=\frac{-4}{9}-\frac{1}{5}\\ x=\frac{-29}{45}\end{array}$

b) $\frac{5}{7}-x=-\frac{9}{21}$

$\begin{array}{l}x=\frac{5}{7}+\frac{9}{21}\\ x=\frac{8}{7}\end{array}$