How do you solve #(x - 4)(x + 5) = 7# using the quadratic formula?

1 Answer
Jarni Renz
Feb 20, 2016

#x=(-1 +-sqrt109)/2#

Explanation:

  1. Simplify the equation by FOIL METHOD
    #(x-4)(x+5)=7#
    #x^2+5x-4x-20=7#
    #x^2+x-27=0
  2. Identify the values for a, b, and c
    #a=1#
    #b=1#
    #c=-27#
  3. Use the standard formula, which is
    #x=(-b+-sqrt(b^2-4ac))/(2a)#
  4. Plug in the values
    #x=(-1+-sqrt(1^2-4(1)(-27)))/(2(1))#
    #x=(-1+-sqrt(1+108))/2#
    #x=(-1+-sqrt109)/2#
  5. Answer
    #x=(-1+-sqrt109)/2#
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