How do you solve the quadratic #x^2+3x-28=0# using any method? Precalculus Linear and Quadratic Functions Completing the Square 1 Answer Mahendra S. · EZ as pi Aug 31, 2016 #x= 4, -7# Explanation: #x^2 +3 x -28 = 0# #x^2 +7 x - 4 x -28= 0# #x ( x+7 ) -4 (x + 7 ) = 0# #( x+7) ( x-4 ) = 0# Either # ( x+7) = 0, or ( x-4) = 0# If # x+7 = 0# #x = -7# If #x-7 = 0# #x= 4# #x = 4 , -7# 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 8280 views around the world You can reuse this answer Creative Commons License