The figure shows a triangle ABC with the
incircle I and the excircles E_{A} and E_{C} tangent to the sides
AC, BC, and AB at the points B', C' and A', respectively. Prove that AA', B'B,
and CC' concur in the outer Nagel point N_{B}.
Christian Heinrich von Nagel (28 February 1803, Stuttgart, Germany – 27 October 1882, Ulm, Germany) was a German geometer.
