How do you solve x^2-4x=6 algebraically?

$x = 4 \pm \sqrt{10}$
$y = {x}^{2} - 4 x - 6 = 0$
$D = {d}^{2} = {b}^{2} - 4 a c = 16 + 24 = 40$ --> $d = \pm 2 \sqrt{10}$
$x = - \frac{b}{2 a} \pm \frac{d}{2 a} = \frac{8}{2} \pm \frac{2 \sqrt{10}}{2} = 4 \pm \sqrt{10}$