Parabola as Envelope
The parabola is the locus of points in that plane that are equidistant from a line, called directrix and a fixed point, called focus.
Another way to view the graph of a parabola is by constructing its envelope, that is the set of all the tangent lines at any point of it.
In the following app you can:
- set the position of the directrix by moving the two diamond points that define it
- set the position of the focus by dragging point
- start or pause the animation using the button on the bottom left, or move the green point along the directrix to animate the construction manually
- delete the trace of the envelope, using the button on top right