How do you solve the quadratic #x^2+9x+20=0# using any method? Precalculus Linear and Quadratic Functions Completing the Square 1 Answer George C. Aug 17, 2016 #x=-4# or #x=-5# Explanation: Note that #4+5=9# and #4*5=20# So: #0 = x^2+9x+20 = (x+4)(x+5)# Hence zeros: #-4, -5# Answer link Related questions What does completing the square mean? How do I complete the square? Does completing the square always work? Is completing the square always the best method? Do I need to complete the square if #f(x) = x^2 - 6x + 9#? How do I complete the square if #f(x) = x^2 + 4x - 9#? How do I complete the square if the coefficient of #x^2# is not 1? How do I complete the square if #f(x) = 3x^2 + 12x - 9#? If I know the quadratic formula, why must I also know how to complete the square? How do I use completing the square to describe the graph of #f(x)=30-12x-x^2#? See all questions in Completing the Square Impact of this question 8531 views around the world You can reuse this answer Creative Commons License