Once you finish a book on geometry, everyone wants help. 🙂

I wound up making this short video on how to find the center of a circle for my dad.  It’s not ideal; I need a better set-up for making videos at my desk.  But the essence of it are these steps:

  1. On a given circle, find three points about 1/3 of the way around the circle, A, B, and C.
  2. Arc the distance AB center A, and BA center B, so the arcs overlap one another at two points, D and E.  Draw a line between D and E — the center will be on that line.
  3. Arc the distance AC center A, and CA center C, so the arcs overlap one another at points F and G.  Draw the line between D and E — the center has to be on that line.
  4. Point O is the place where lines DE and FG cross. That’s the center of the circle.

I hope this helps!