Determining Whether a Point Lies on a Circle The point 4 0 lies on a circle that is centered at the origin Does the point 2 12 also lie on the circle d x x y y All radii of a circle have the same length r 4 R Is 2 12 4 units from the center x y 0 x2 y 2 4 2 0 12 0 16 Yes the point does lie on the circle 5 5 4 3 2 1 4 2 0 0 1 2 7 5 y 1 2 3 31 5