1)
$4x^2+3(2x^2+1)=2x(5x-7)$
$⇔4x^2+6x^2+3=10x^2-14x$
$⇔4x^2+6x^2-10x^2+14x=-3$
$⇔14x=-3$
$⇔ x=-\frac{3}{14}$
Vậy $S={-\frac{3}{14}}$
2)
$x(x^2-7)=2x(\frac{1}{2}x^2+6)+8$
$⇔x^3-7x=x^3+12x+8$
$⇔x^3-x^3-7x-12x=8$
$⇔-19x=8$
$⇔ x=\frac{-8}{19}$
Vậy $S={\frac{-8}{19}}$