Hi all, i hope this is the right place.

I'am trying to do some rotation in a 3D space, basically i have 3 nodes (a,b,c) and two edges (a,b),(b,c). I'am trying to rotate along i believe the axis formed by the edge (b,c) with the aim of repositioning node 'a' along the circular plane.

http://cdr.wolfe.googlepages.com/rotate.gif
What i was hoping someone maybe able to help me with is, i need to basically 'randomly' place node 'a' along various parts of the circular plane, but need to keep the angle and length constraints the same obviously.

If i have the X,Y,Z coordinates for all nodes (a,b,c) along with length of edges, is thre a way i can use them to place 'a' somewhere along the circular polane but remain within constraints?

Any help is appreciated, trust me :D

Regards Wolfe