Envelope Curve

Animate By and watch how the perpendicular bisector of AB moves.
Now turn on the trace using teh slider to see multiple locations at once.
Turn on the envelope curve with its slider to see the curve tangential to the entire family of lines.

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Ay
Trace
0 0 1
Curve
0 0 1
Bx
-6 0 6

Make Ay smaller and observe how the curve changes.