Spherical Law of Sines

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Draw a spherical triangle on the surface of the unit sphere with center at the origin
. Let the sides (arcs) opposite the vertices have lengths
,
and
, and let
,
and
be the angles at the vertices
,
and
. The spherical law of sines states that
.
Contributed by: Izidor Hafner (February 2017)
Open content licensed under CC BY-NC-SA
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Details
Let be the orthogonal projection of
onto the plane
. Let
and
be the orthogonal projections of
onto the lines
and
, respectively. Then
,
,
,
and
, so
.
References
[1] Wikipedia. "Spherical Law of Cosines." (Feb 22, 2017) en.wikipedia.org/wiki/Spherical_law_of _cosines.
[2] Wikipedia. "Spherical Trigonometry." (Feb 22, 2017) en.wikipedia.org/wiki/Spherical_trigonometry.
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