How do you solve x^2 - x - 30 = 0 using the quadratic formula?

1 Answer
Alan P.
Feb 24, 2016

See below for use of quadratic formula to obtain
x=-5 or x=6

Explanation:

For the general quadratic equation ax^2+bx+c=0
the quadratic formula:
color(white)("XXX")x=(-b+-sqrt(b^2-4ac))/(2a)
gives the solutions.

For the example: x^2-x-30=0
color(white)("XXX")a=1
color(white)("XXX")b=-1
color(white)("XXX")c=-30

Replacing the variables a, b, c in the general solution formula gives:
color(white)("XXXX")x=(-(-1)+-sqrt((-1)^2-4(1)(-30)))/(2(1))

color(white)("XXXX")=(1+-sqrt(121))/2

color(white)("XXXX")=(1+-11)/2

rArr x=-5 or +6

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