Law of tangents
In
trigonometry, the
law of tangents is a statement about arbitrary triangles in the plane. If two sides of a triangle are (lowercase)
a and
b and the
angles opposite those sides are (capital)
A and
B, then the law of tangents states
Derivation
Start with (a + b)/(a  b). ((sin A)/a = (sin B)/b because of the law of sines):

 (See: Trigonometric identity)
See also: