$x^2 - 25 = 0$
$x^2 = 25$
$x = \pm 5$

$0.2x^2 + 7.2 = 0$
$0.2x^2 = -7.2$
$x^2 = -36$
No real solutions.

$-7x^2 + 28 = 0$
$-7x^2 = -28$
$x^2 = 4$
$x = \pm 2$

$-4x^2 + 1 = 0$
$-4x^2 = -1$
$x^2 = \frac{1}{4}$
$x = \pm \frac{1}{2}$

$-0.8x^2 - 9.2 = 0$
$-0.8x^2 = 9.2$
$x^2 = \frac{9.2}{0.8} = 11.5$
$x = \pm \sqrt{11.5}$

$-0.1x^2 + 10 = 0$
$-0.1x^2 = -10$
$x^2 = 100$
$x = \pm 10$