The document describes a visit to the Abbatiale Saint Etienne during a 2012 Comenius meeting in France. Three stones in the wall of the abbatiale are arranged in a partial circle formation. The document also provides an exercise involving measuring the arc lengths and distance between two circles to determine the radius of the smaller circle. A second exercise asks to establish a general formula for calculating the radius.

1. Comenius Abbatiale Saint Etienne Dipl.-Math. T. Günther
At the 2012 Comenius meeting in France we visited the Abbatiale Saint Etienne.
Three stones of its wall are arranged in a (part of an) circle:
1. Exercise: The arclength b1 and b2 and the distance d of the two circles can be meassured: b1 = 60cm, b2 = 70cm and
d = 25cm (see sketch above). Determine the radius r of the smal circle.
2. Exercise: Establish a formula for the radius r in general case.