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 8752 views around the world You can reuse this answer Creative Commons License