Tìm x: 2(x^2 + 8x +16) -x - 4 = 0

* Hướng dẫn giải

$\begin{array}{l}2\left({\mathrm{x}}^2+8\mathrm{x}+16\right)-\mathrm{x}-4=0\\ \Rightarrow 2{\left(\mathrm{x}+4\right)}^2-\left(\mathrm{x}+4\right)=0\\ \iff \left(\mathrm{x}+4\right)\left[2\left(\mathrm{x}+4\right)-1\right]=0\\ \left(\mathrm{x}+4\right)\left(2\mathrm{x}+7\right)=0\Rightarrow \left[\begin{array}{l}\mathrm{x}=-4\\ \mathrm{x}=-\frac{7}{2}\end{array}\right.\end{array}$