How do I use the quadratic formula to solve #f(x) = 4x^2 + 12x + 9#? Precalculus Linear and Quadratic Functions The Quadratic Formula 1 Answer AJ Speller Sep 30, 2014 #ax^2+bx+c=0# #4x^2+12x+9=0# #a=4, b=12, c=9# Quadratic formula #x=(-(12)+-sqrt((12)^2-4(4)(9)))/(2(4))# #x=(-12+-sqrt(144-144))/8# #x=(-12+-sqrt(0))/8# #x=(-12)/8# #x=-3/2# #x=-1.5# Answer link Related questions What are common mistakes students make when using the quadratic formula? What do the variables in the quadratic formula mean? What are the possible outcomes when using the quadratic formula? How do I use the quadratic formula to solve #f(x) = x^2 + 3x - 2#? How do I use the quadratic formula to solve #f(x) = x^2 + 3x - 7#? What is the discriminant of a quadratic function? Can the quadratic formula be used to solve a linear equation? How do I use the quadratic formula to solve #3x^2 - 6 = 4x#? How do I use the quadratic formula to solve #4x^2+x-1=0#? How do I use the quadratic formula to solve #5x^2+9x-2=0#? See all questions in The Quadratic Formula Impact of this question 4068 views around the world You can reuse this answer Creative Commons License