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Ploščina (Area) trikotnika na sferi:
A, B, C = angles of spherical triangle in degrees
E = spherical excess of triangle, E = A + B + C - 180
- other formula for the spherical excess E
a, b, c = sides of spherical triangle
s=(a+b+c)/2
tan(E/4) = sqrt(tan(s/2)*tan((s-a)/2)*tan((s-b)/2)*tan((s-c)/2))
Area = pi*R^2*E/180
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