point on a circle extract dx and dy?

Question

Given a circle like this, where i know the 2d coordinates of the center, and the radius of the circle, how do i determine the point on the circle, of more precise, dx and dy?

illustration

Sorry for my immature drawing skills.

Answer 1

Say $O_x$ and $O_y$ are the coordinates of the center and $r$ is its radius.
Then you have:

$(dx-O_x)^2 + (dy-O_y)^2 = r^2$

Any couple $(dx,dy)$ satisfying this equation is a point from the circle.
Of course you cannot determine $(dx,dy)$ uniquely, since there're many points on that circle.