Menelaus' and Ceva's Theorem for Spherical Triangle
Draw a spherical triangle on the surface of a unit sphere centered at . Let the sides opposite the corresponding vertices be the arcs , , and contain the points , , . Menelaus's theorem for a spherical triangle states:[more]
The rays , , are on the same plane if and only if
Ceva's theorem for a spherical triangle states:
The planes determined by pairs of rays , and go through the same ray () if and only if
A proof of these theorems can be found in [3, pp. 85–86].
 Wikipedia. "Spherical Law of Cosines." (Mar 20, 2017) en.wikipedia.org/wiki/Spherical_law_of _cosines.
 Wikipedia. "Spherical Trigonometry." (Mar 20, 2017) en.wikipedia.org/wiki/Spherical_trigonometry.
 V. V. Prasolov and I. F. Sharygin, Problems in Stereometry (in Russian), Moscow: Nauka, 1989.