Law of Sines

Theorem
For any triangle $\triangle ABC$:


 * $\dfrac a {\sin A} = \dfrac b {\sin B} = \dfrac c {\sin C}$

where $a$, $b$, and $c$ are the sides opposite $A$, $B$ and $C$ respectively.

Also known as
This result is also known as the sine law, sine rule or rule of sines.

Historical Note
This was documented by Nasīr al-Dīn al-Tūsī in his work On the Sector Figure, part of his five-volume Kitāb al-Shakl al-Qattā (Book on the Complete Quadrilateral).