tìm x: (x-4) (5x-2) - 3(4-x) = 0

* Hướng dẫn giải

$\begin{array}{l}\left(x-4\right)\left(5x-2\right)-3\left(4-x\right)=0\\ 5x^2-20x-2x+8-12+3x=0\\ 5x^2-19x-4=0\\ 5x^2-20x+x-4=0\\ 5x\left(x-4\right)+\left(x-4\right)=0\\ \left(x-4\right)\left(5x+1\right)=0\Rightarrow \left[\begin{array}{l}x=4\\ x=-\frac{1}{5}\end{array}\right.\end{array}$