tìm x, biết :...

LTKH

$\left(\frac{2}{5}x\right)\left(\frac{15x}{2}+\frac{1}{4}\right)-\left(3x^2+x+2\right)=5$

$\frac{2}{5}x\cdot\frac{15x}{2}+\frac{2}{5}x\cdot\frac{1}{4}-\left(3x^2+x+2\right)=5$

$3x^2+\frac{1}{10}x-3x^2-x-2=5$

$\left(3x^2-3x^2\right)+\left(\frac{1}{10}x-x\right)-2=5$

$-\frac{9}{10}x=7$

$x=\frac{7}{-\frac{9}{10}}=\frac{7\cdot10}{-9}=-\frac{70}{9}$