Tìm x biết a) x+ 3/7 = -2/7 b) 1/12 +x = -2/3

* Hướng dẫn giải

a) 

$\begin{array}{l}x+\frac{3}{7}=\frac{-2}{7}\\ x=\frac{-2}{7}-\frac{3}{7}=\frac{-5}{7}\end{array}$

b)

$\begin{array}{l}\frac{1}{12}+x=\frac{-2}{3}\\ x=\frac{-2}{3}-\frac{1}{12}=\frac{-8}{12}-\frac{1}{12}=\frac{-9}{12}=\frac{-3}{4}\end{array}$