Half-side formula
Encyclopedia
Spherical trigonometry
Spherical trigonometry is a branch of spherical geometry which deals with polygons on the sphere and the relationships between the sides and the angles...
, the half side formula relates the angles and lengths of the sides of spherical triangles, which are triangles drawn on the surface of a sphere and so have curved sides and do not obey the formulas for plane triangles.
Formulas
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where- a, b, c are the lengths of the sides respectively opposite α, β, γ,
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is half the sum of the angles, and -
The three formulas are really the same formula, with the names of the variables permuted.