How do you solve $0 = x^2 + x - 20$ using the quadratic formula?

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Answer 1 · 2016-03-20T16:35:59

The solutions are:
$x = 4$

$x = -5$

$0 = x^2 + x -20$

$x^2 + x -20 = 0$

The equation is of the form $color(blue)(ax^2+bx+c=0$ where:
$a=1, b=1, c=-20$

The Discriminant is given by:

$Delta=b^2-4*a*c$

$= (1)^2-(4 * 1 * ( - 20 ) )$

$= 1 + 80 = 81$

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

$x = ((-1)+-sqrt(81))/(2*1) = (-1+-9)/2$

$x= (-1+9)/2 = 8/2 = 4$

$x= (-1 -9) /2 = (-10)/2 = -5$

How do you solve 0 = x^2 + x - 200 = x^2 + x - 20 using the quadratic formula?