# How do you graph y = x² + 2x – 4?

Aug 16, 2015

Graph y = x^2 + 2x - 4

#### Explanation:

To graph a parabola, find a few critical points:
Axis of symmetry --> $x = - \frac{b}{2} a = - 1$
Vertex --> $x = - \frac{b}{2} a = - 1$
y = f(-1) = 1 - 2 - 4 = -5
y-intercept --> make x = 0 --> y = -4
x-intercept --> solve y = 0 --> ${x}^{2} + 2 x - 4 = 0.$
$D = {d}^{2} = {b}^{2} - 4 a c = 4 + 16 = 20$-->$d = \pm 2 \sqrt{5}$
$x = - \frac{2}{2} \pm 2 \frac{\sqrt{5}}{2} = - 1 \pm \sqrt{5}$
graph{x^2 + 2x - 4 [-10, 10, -5, 5]}