Find the blanks, and answer

$x (-0.5) x = -20$

$-0.5{x}^{2}=-20$

${x}^{2}=\frac{-20}{-0.5}$

${x}^{2}=40$

$x=\sqrt{40}$

$x= 2\sqrt{10} , x=-2\sqrt{10}$