How do you solve #x^2 - 2x - 18 = 0# using the quadratic formula?

1 Answer
Aug 6, 2015

Answer:

#x= 1+sqrt(19)# or #x=1-sqrt(19)#
(see below for solution using the quadratic formula)

Explanation:

The quadratic formula says that for any quadratic in the form:
#color(white)("XXXX")##ax^2+bx+c=0#
the roots (solution) can be determined by:
#color(white)("XXXX")##x= (-b+-sqrt(b^2-4ac))/(2a)#

For the given equation #x^2-2x-18=0#
#a=1##color(white)("XXXX")##b=-2##color(white)("XXXX")##c=-18#

So the solutions are
#color(white)("XXXX")##x=(2+-sqrt((-2)^2-4(1)(-18)))/(2(1))#

#color(white)("XXXX")##color(white)("XXXX")##= (2+-sqrt(4+72))/2#

#color(white)("XXXX")##color(white)("XXXX")##=(2+-sqrt(76))/2#

#color(white)("XXXX")##color(white)("XXXX")##=(2+-2sqrt(19))/2#

#color(white)("XXXX")##color(white)("XXXX")##= 1+-sqrt(19)#