# How do you solve x^2 - 3x - 4 = 0 using the quadratic formula?

Jul 22, 2015

Identify the coefficients $a$, $b$ and $c$ and substitute those values into the quadratic formula to find $x = - 1$ or $x = 4$.

#### Explanation:

${x}^{2} - 3 x - 4 = 0$ is of the form $a {x}^{2} + b x + c = 0$, with $a = 1$, $b = - 3$ and $c = - 4$.

The quadratic formula gives us solutions:

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

$= \frac{3 \pm \sqrt{{3}^{2} - \left(4 \times 1 \times - 4\right)}}{2 \cdot 1}$

$= \frac{3 \pm \sqrt{9 + 16}}{2}$

$= \frac{3 \pm \sqrt{25}}{2}$

$= \frac{3 \pm \sqrt{{5}^{2}}}{2}$

$= \frac{3 \pm 5}{2}$

That is $x = - 1$ or $x = 4$