Statics: Rigid Body Equilibrium

[Chandasouk]

Hello, I was wondering if someone could explain part of the solution to this problem for me.

http://img706.imageshack.us/img706/5517/disksproblem.png

To the right is the Free Body Diagram of Disk E, and I can draw the forces on there well enough. But I really do not understand how they obtained that triangle for N' (1-5-√24). I know this is the force of disk D acting on disk E, but that's about it.

 

[SteamKing]

When two circles touch, the point of contact lies on a line joining the centers of the two circles. Using the two radii and some geometry, you can derive the components of the N' vector.