How do you solve $x^2 − 8x − 4 = 0$ using the quadratic formula?

Question

22515 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2015-08-10T07:32:04

The solutions for the equation are:
$color(blue)(x=4+2sqrt5$
$color(blue)(x=4-2sqrt5$

$x^2−8x−4=0$

The equation is of the form $color(blue)(ax^2+bx+c=0$ where:
$a=1, b=-8, c=-4$

The Discriminant is given by:
$Delta=b^2-4*a*c$

$= (-8)^2-(4*(1)*-4)$

$= 64+16$

$=80$

The solutions are found using the formula
$x=(-b+-sqrtDelta)/(2*a)$

$x = (-(-8)+-sqrt(80))/(2*1) = (8+-4sqrt(5))/2$

$x=(cancel2(4+-2sqrt(5)))/cancel2$

$x=4+-2sqrt5$

The solutions are
$color(blue)(x=4+2sqrt5 , color(blue)(x=4-2sqrt5$

How do you solve x^2 − 8x − 4 = 0x^2 − 8x − 4 = 0 using the quadratic formula?