Prove that

If the sides of a triangle are in arithmetic progression if and only if the cotangents of its half-angles

, ,

are also in arithmetic progression

Also, if and only if

The sequence of the squares of the side lengths is in arithmetic progression if and only if

, , is also an arithmetic progression.

Trigonometric proof using the Law of cotangents

Trigonometry/Solving triangles by half-angle formulae

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## About benvitalis

math grad - Interest: Number theory