Originally Posted by Avistew
Just want to point out that it doesn't have to be an ellipse, it CAN be a circle with A as not-the-center.
Here is an example, and I showed where the center is, too.
I could still assume it's a quarter of a circle/elipse if A were in the first quadrant (Top - left part of the center). It's not, so, in this case AD can't be related to a Radius of an imaginary circle, so, I can't solve this problem if I don't know the lenght of either AB or AC (Nope, either knowing AF or AE will help us in that case, because we'll still missing AB and AC).