Tìm x: x^2 - 25 + 2(x+5) = 0

* Hướng dẫn giải

$\begin{array}{l}{\mathrm{x}}^2-25\mathrm{x}+2\left(\mathrm{x}+5\right)=0\\ \left(\mathrm{x}-5\right)\left(\mathrm{x}+5\right)+2\left(\mathrm{x}+5\right)=0\\ \left(\mathrm{x}+5\right)\left(\mathrm{x}-5+2\right)=0\\ \left(\mathrm{x}+5\right)\left(\mathrm{x}-3\right)=0\\ \Rightarrow \left[\begin{array}{l}\mathrm{x}+5=0\\ \mathrm{x}-3=0\end{array}\right.\iff \left[\begin{array}{l}\mathrm{x}=-5\\ \mathrm{x}=3\end{array}\right.\end{array}$