The figure shows a triangle ABC with
semiperimeter s and the excircles E_{A}, E_{B}, and E_{C} tangent to the sides at the points A', B', C',
A_{1}, A_{2}, B_{1}, B_{2}, C_{1},
and C_{2}. Prove that s = AA_{1} = AA_{2} = BB_{1}
= BB_{2} = CC_{1} = CC_{2}.
