



 
Craige, The relationship involving the arc length a the radius of the circle r and the angle θ measured in radians is
I let the inside radius be r, the length of the inside arc be a_{1} and the length of the outside arc be a_{2}. Then for the inside arc
and for the outside arc
Since the angle θ is the same for both arcs
Solving for r gives
Harley  


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