Thank you for taking time to read my post, I hope I am putting into the correct area of the physics forum. I am working with a programmer to complete a project that involves 2 intersecting vectors and a circle. The vector coordinates are known, we are trying to solve the circle equation. I have provided a visual example. The programmer says the problem is he needs a 4th point in order to program this and is not sure how to do this. He states the following: The equation of ellipse is: (X -Xo)^2/A^2 + (Y-Yo)^2/B^2 = 1 where Xo,Yo - coordinates of center, A - major, B - minor semiaxes http://curezone.com/ig/i.asp?i=69998 Thanks again.