Tìm x, biết: ( x+ 1/5)^2 =9

* Hướng dẫn giải

$\begin{array}{l}a)x\in \left\{\frac{14}{5};\frac{-16}{5}\right\}\\ \\ b)x\in \left\{\frac{-1}{6};\frac{-5}{6}\right\};\\ \\ c)x\in \left\{\frac{7}{15};\frac{-2}{15}\right\}\\ \\ d)x=\frac{2}{3}\end{array}$