There are 2 cogs, connected together by 1 belt. Find the length of the belt.

The large cog has a radius of 11cm. The small cog has a radius of 4cm. The distance between the centre of the 2 cogs is 25cm.

(Diagram not drawn to scale)

http://www.mathhelpforum.com/math-he...og-problem.png
I'm stuck because I cannot solve the angle AOB or YPZ, and I cannot solve the length of AY or BZ. Once I get those, then I can get solve the answer.

Can anyone tell me how to get the angle or length?

Does the angle AOB = angle YPZ?

I got $\displaystyle 147.48^{\circ}$ for angle AOB and $\displaystyle 212.52^{\circ}$ for the reflex angle of YPZ because I assumed they were equal, but it doesn't seem right.