Parabolas from Rays

points

3

This Demonstration shows how to draw the half parabola that includes a given point, has directrix parallel to the

x

axis, and has its vertex at the origin. First divide the area between the

y

axis and the given point into

k

strips by

k-1

parallels to the

y

axis. Then draw rays from the origin to

k-1

points between the given point and the

x

axis. The

k-1

pairwise intersections of parallels and rays are points of the parabola.