# How do you solve 3x^2+9x-12=0 using the quadratic formula?

Feb 15, 2016

Solution is $x = 1 \mathmr{and} - 4$.

#### Explanation:

Solution of quadratic equation $a {x}^{2} + b x + c = 0$ is given by

$x = \frac{- b \pm \sqrt{{b}^{2} - 4 a c}}{2 a}$

Here $a = 3 , b = 9 \mathmr{and} c = - 12$. Putting these values

$x = \frac{- 9 \pm \sqrt{{9}^{2} - 4 \cdot 3 \cdot \left(- 12\right)}}{2 \cdot 3}$

= $x = \frac{- 9 \pm \sqrt{81 + 144}}{6}$

= $x = \frac{- 9 \pm \sqrt{225}}{6}$ = $x = \frac{- 9 \pm 15}{6}$

= $1 \mathmr{and} - 4$