Tìm x biết: 49x^2 - 1 = 0

* Hướng dẫn giải

$\begin{array}{l}49{\mathrm{x}}^2-1=0\\ \left(7\mathrm{x}-1\right)\left(7\mathrm{x}+1\right)=0\\ \Rightarrow \left[\begin{array}{l}7\mathrm{x}-1=0\\ 7\mathrm{x}+1=0\end{array}\right.\Rightarrow \left[\begin{array}{l}\mathrm{x}=\frac{1}{7}\\ \mathrm{x}=-\frac{1}{7}\end{array}\right.\\ \end{array}$