# How do I use the quadratic formula to solve f(x) = 4x^2 + 12x + 9?

Sep 30, 2014

$a {x}^{2} + b x + c = 0$

$4 {x}^{2} + 12 x + 9 = 0$

$a = 4 , b = 12 , c = 9$

$x = \frac{- \left(12\right) \pm \sqrt{{\left(12\right)}^{2} - 4 \left(4\right) \left(9\right)}}{2 \left(4\right)}$

$x = \frac{- 12 \pm \sqrt{144 - 144}}{8}$

$x = \frac{- 12 \pm \sqrt{0}}{8}$

$x = \frac{- 12}{8}$

$x = - \frac{3}{2}$

$x = - 1.5$