I solve that problem but I don't understand why I should take 2*Pi*R ?
I know that the center length of the center of the nails is:
sqrt((x2-x1)^2 + (y2-y1)^2)
but why 2*PI*R ??????

Edited by author 31.10.2004 17:26

help me. i can't solve this problem.

2PiR is length of arc's

it has a very nice solution

You should find explanations to the formula to not
it be trick.
For example. Let us consider inner normal vector to the boundary - n , moving along boundary. It gets rotation 2*Pi after one circle. But really n rotates only on angles or on
archs and total rotation is L/R where L- total length of archs . Thus we have 2*Pi=L/R therefore L=2*Pi*R