The Law of Cosines in Spherical Trigonometry
Let A,B,C be the vertex angles of a spherical
triangle on the unit sphere, and a,b,c the
lengths of the opposite sides, measured by the
angles they subtend at the center.
SPHERICAL LAW OF COSINES:
cosa = cosb cosc + sinb sinc cosA.
(There is also the
SPHERICAL LAW OF SINES:
sina / sinA = sinb / sinB =
sinc / sinC.)
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