Tangent 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 tangent is a theorem connecting the tangents of two angles of a triangle and the lengths of sides opposite to these angles. The tangent theorem, although not as widely known as the sine theorem or the cosine theorem, is quite useful, and can be used in cases where two sides and one angle are known, or, conversely, two angles and one side.