Please consider the figure below:

I hope I am asking my Question in right forum.. I want to get set of paired points on circle using diameter. What I have is center point of circle and its diameter.
Consider black line in figure. Line is passing through center, as well as equal to diameter of circle. Red and green lines are same, only the difference is of points used/angle. Can anyone tell me a formula or solution to get random paired points on circle. I hope my Question is clear. Thanks.