Whose equation is this?
Answer
This is Mollweide’s formula
In trigonometry, Mollweide’s formula, sometimes referred to in older texts as Mollweide’s equations, named after Karl Mollweide, is a set of two relationships between sides and angles in a triangle. It can be used to check solutions of triangles.
Let a, b, and c be the lengths of the three sides of a triangle. Let α, β, and γ be the measures of the angles opposite those three sides respectively. Mollweide’s formula also states that
Each of these identities uses all six parts of the triangle – the three angles and the lengths of the three sides.