
 Trigonometry 
  Since the proof of the spherical Law of Tangents is identical to that of the correspoinding plane Law of Tangents, we state the spherical Law of Tangents without proof. 
  An interesting problem of spherical trigonometry is that of finding the area of a spherical cap of either a cone or pyramid, with its apex at the center of the sphere. 
  For each law, we give the spherical (a, b, c are the sides; A, B, C are the angles), its dual for the polar triangle (A. C are the angles; a, b, c are the sides), and the plane (a, b, c are the norms of the sides; A, B, C are the angles) version. 
 www.rism.com /Trig/Trig02.htm (8729 words) 
