Tìm x biết x- 1/2=7/13.13/28

* Hướng dẫn giải

$\begin{array}{l}a)x-\frac{1}{2}=\frac{7}{13}.\frac{13}{28};x-\frac{1}{2}=\frac{1}{4}\\ \\ b)\frac{x}{15}=\frac{-3}{11}.\frac{77}{36};\frac{x}{15}=\frac{-7}{12};x=15.\frac{-7}{12}\\ \\ c)x+\frac{7}{7}=\frac{9}{18}.\frac{9}{27};x+1=\frac{1}{6}\\ \\ d)x:\frac{15}{11}=\frac{-3}{12}.8;x:\frac{15}{11}=-2;x=(-2).\frac{15}{11}\end{array}$