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

1 Answer
Mar 20, 2016

Answer:

The solutions are:
#x = 4#

#x = -5#

Explanation:

# 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#