Sunday, August 24, 2014

Parabola focus and directrix

From http://www.mathopenref.com/parabolafd.html
http://www.softschools.com/math/calculus/writing_the_equation_of_parabolas/

One of the ways to define a parabola -

 the locus of all points that are equidistant from a given point (focus) and a given line (directrix).






















To write the equation of a parabola....

1. Determine which pattern to use (based on whether it is horizontal or vertical)

2. Substitute in h and k ,which is the vertex of the parabola.

3. Choose a coordinate to substitute in and solve for a.

4. Write your final equation with a, h, and k.


Remember the patterns: 

To derive, see http://www.mathopenref.com/parabolafdderive.html


   
    Using the focus and directrix to find the equation of a parabola:





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