How to find degree on a circle that is tangent to a point outside of that circle? : - I know the (x,y) of a point, P, outside of a circle.
- I know the (x,y) for the origin of a circle, O.
- I know the radius, r, of that circle.

How would I find what degree (i.e. 20 degrees, 270 degrees) is tangent to the point outside of the circle ?

[click here for an image][1]


  [1]: https://i.stack.imgur.com/eVbc1.png


Many thanks in advance!
-joe