`(2x - 1)^{2} = 49`
$\Rightarrow$ `(2x - 1)^{2} = (+- 7)^{2}`
$\Rightarrow$ $\left[\begin{matrix} 2x-1=7\\ 2x-1=-7\end{matrix}\right.$
$\Rightarrow$ $\left[\begin{matrix} 2x=7+1\\ 2x=-7+1\end{matrix}\right.$
$\Rightarrow$ $\left[\begin{matrix} 2x=8\\ 2x=-6\end{matrix}\right.$
$\Rightarrow$ $\left[\begin{matrix} x=8:2\\ x=-6:2\end{matrix}\right.$
$\Rightarrow$ $\left[\begin{matrix} x=4\\ x=-3\end{matrix}\right.$
$\text{Vậy}$ `x \in {4 ; -3}`
