9.2 Parabolas Emerald Seing
A parabola is defined in terms of a fixed point, the focus, and a fixed line, the directrix. PF=PD meaning that any point on the parabola to the focus is equal to the shortest distance from that point to the directrix.
Finding The Equation
This is only true for equations with the center at (0,0).
Horizontal Directrix Vertical Directrix The parabola will open either up or down The equation will have Y by itself on one side The line of the directrix will cross the Y-axis The axis of symmetry will be on the Y-axis Y=… Vertical Directrix The parabola will open either right or left The equation will have X by itself on one side The line of the directrix will cross the X-axis The line of symmertry will be on the X-axis X=…
Example One
Example Two
These equations apply to all parabolas who’s centers are not located at (0,0).
Example One
Example Two