Y is on the middle perpendicular on PX and on the perpendicular through X to the line. So Y has the same distance to P and to the line.

Der Punkt Y liegt auf der Mittelsenkrechten auf PX und auf dem Lot durch X zur Geraden. Also ist Y von P genauso weit entfernt wie von der Geraden.

Now, generate the automatic track of Y, when X moves. The track is a parabola, which is turned to the left. I will try to convince you, that it is indeed a parabola.

Note that the middle perpendicular is always tangent to the parabola.

For a change, track the middle perpendicular (instead of the point Y), when X runs on the line. This is indeed possible, and C.a.R. will compute a curve, such that all middle perpendiculars are tangent to the curve. So, select the automatic track tool, click on the middle perpendicular and then on X.

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