C.a.R. >
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Conic Sections > **
Parabola with Focus**

The track of all points with equal distance to a given point
and a line is a parabola. You can move the point and the point on the line. Move
with the right mouse button to snap to grid points. Note that the green angles
are equal. This is, why the point is called the focal point.

### Technical Information

The parabola is a track here. The function expression is a
bit tricky, since we want to avoid x--1 and get x+1 instead. Moreover, the green
angles you see are different on the right and on the left. They are hidden, if
they become larger than 90° using conditional formatting.