Giải phương trình sau : (2,1x - 1,2)^2 - 0,25 = 0

* Hướng dẫn giải

$\begin{array}{l}{\left(2,1x-1,2\right)}^2-0,25=0\\ \iff {\left(2,1x-1,2\right)}^2-0,5^2=0\\ \iff \left(2,1x-1,2-0,5\right)\left(2,1x-1,2+0,5\right)=0\\ \iff \left(2,1x-1,7\right)\left(2,1x-0,7\right)=0\\ \iff \left[\begin{array}{l}2,1x-1,7=0\\ 2,1x-0,7=0\end{array}\right.\iff \left[\begin{array}{l}x=\frac{17}{21}\\ x=\frac{1}{3}\end{array}\right.\end{array}$