Cotangent theorem

Theorem in geometry is a proof - an argument establishing a property. A theorem is a statement that proves some property and requiring establishment. Theorems are also called lemmas, properties, consequences, rules, signs, affirmations.

The law of cotangent is a trigonometric theorem connecting the radius of an inscribed circle of a triangle with the length of its sides. The cotangent theorem is convenient to use when solving a triangle on three sides.