Constructing a Parabola from Tangent Circles

radius of inner circle

10

distance of inner circle from line

5

Let

C

be a circle that does not intersect a horizontal line

l

. Use the sliders to change the radius of

C

or the distance of

C

to

l

. The locus of the centers of the circles that are tangent to both

C

and

l

is a parabola.