tangents law

Let $ABC$ be a triangle with $a,b$ and $c$ being the sides opposite to $A,B$ and $C$ respectively. Then the following relation holds.

$$\frac{a-b}{a+b}=\frac{\tan (\frac{A-B}{2})}{\tan (\frac{A+B}{2})}.$$

Title	tangents law
Canonical name	TangentsLaw
Date of creation	2013-03-22 13:11:01
Last modified on	2013-03-22 13:11:01
Owner	giri (919)
Last modified by	giri (919)
Numerical id	5
Author	giri (919)
Entry type	Theorem
Classification	msc 51-00
Synonym	law of tangents