Let L and N be adjacent cusps of a cycloid.
Let P be a point on the cycloid between L and N.

Construct with straightedge and compass the tangent line to the cycloid at point P.

Harry's solution is indeed correct.  See  http://www.ies.co.jp/math/java/calc/cycle_ang/cycle_ang.html

Posted by Kenny M on 2010-01-12 00:45:16