How do you solve x^2 = 7x +8 using the quadratic formula?

May 28, 2016

8 and -1

Explanation:

$y = {x}^{2} - 7 x - 8 = 0$
Solving by shortcut. Since a - b + c = 0, then, the 2 real roots are: -1 and -c/a = 8.
$D = {d}^{2} = {b}^{2} - 4 a c = 49 + 32 = 81$ --> $d = \pm 9$
$x = - \frac{b}{2 a} \pm \frac{d}{2 a} = \frac{7}{2} \pm \frac{9}{2} = \frac{7 \pm 9}{2}$
$x = \frac{16}{2} = 8$ and $x = - \frac{2}{2} = - 1$