Trigonometry
Advanced

Law of Tangents

Relates two sides and their opposite angles.

Formula

a−ba+b=tan⁡A−B2tan⁡A+B2\frac{a-b}{a+b} = \frac{\tan\tfrac{A-B}{2}}{\tan\tfrac{A+B}{2}}

Variables

a,bSides
A,BAngles

Did You Know?

The law of tangents predates the more famous law of cosines for solving triangles from two sides and an angle.

law of tangentstriangle