$\frac{1}{7}x^2 = 2x - 7$
$\frac{1}{7}x^2 - 2x + 7 = 0$ |*7
$x^2 - 14x + 49 = 0$
$D = 7^2 - 1 * 49 = 49 - 49 = 0$
x = 7

$x^2 + 1,2 = 2,6x$
$x^2 - 2,6x + 1,2 = 0$
$D = 1,3^2 - 1 * 1,2 = 1,69 - 1,2 = 0,49$
$x = 1,3 ± \sqrt{0,49}$
$x_1 = 1,3 - 0,7 = 0,6$
$x_2 = 1,3 + 0,7 = 2$
Ответ:
$x_1 = 0,6$;
$x_2 = 2$.

$4x^2 = 7x + 7,5$
$4x^2 - 7x - 7,5 = 0$
$D = 7^2 - 4 * 4 * (-7,5) = 49 + 120 = 169$
$x = \frac{7 ± \sqrt{169}}{8}$
$x_1 = \frac{7 - 13}{8} = \frac{-6}{8} = -\frac{3}{4}$
$x_2 = \frac{7 + 13}{8} = \frac{20}{8} = \frac{5}{2} = 2\frac{1}{2}$
Ответ:
$x_1 = -\frac{3}{4}$;
$x_2 = 2\frac{1}{2}$.