Law of Cosines for Spherical Triangles/Sides
- $\cos a = \cos b \cos c + \sin b \sin c \cos A$
Also known as
This result is also known as the Spherical Law of Cosines.
This result was first stated by Regiomontanus in his De Triangulis Omnimodus of 1464.
- 1968: Murray R. Spiegel: Mathematical Handbook of Formulas and Tables ... (previous) ... (next): $\S 5$: Trigonometric Functions: $5.97$
- 2008: Ian Stewart: Taming the Infinite ... (previous) ... (next): Chapter $5$: Eternal Triangles