Book:Nasir al-Din al-Tusi/Kitāb al-Shakl al-Qattā

Nasir al-Din al-Tusi: Kitāb al-Shakl al-Qattā

Published $\text {c. $1250$}$
In English:

Treatise on the Quadrilateral

Subject Matter

• Spherical Trigonometry

Contents

A five volume summary of trigonometry:

The first extant exposition of the whole system of plane and spherical trigonometry

The first work in which all six cases for a right-angled spherical triangle are set forth

Contains the famous Law of Sines:

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

Sources

• 2008: Ian Stewart: Taming the Infinite ... (previous) ... (next): Chapter $5$: Eternal Triangles: Early trigonometry