Evaluate the horizontal parabola
y2 = -12x
Determine coordinates of the focus:
Since our x coefficient of -12 is negative
The parabola opens left
horizontal parabola equation
y2 = 4cx
4c = -12
Divide each side by 4:
| 4c | |
| 4 |
| = |
| -12 |
| 4 |
c = -3
Our focus is (-3,0)
Determine directrix equation:
Directrix is in the form x = c, so we have x = -3
