In geometry, a frustum (plural: frusta or frustums) is the portion of a solid (normally a cone or pyramid) that lies between two parallel planes cutting it. The term is commonly used in computer graphics to describe the three-dimensional region which is visible on the screen, the “viewing frustum”, which  [ Read More ]

According to Ubiratàn D’Ambrosio and Selin Helaine, the spherical law of sines was discovered in the 10th century. It is variously attributed to al-Khujandi, Abul Wafa Bozjani, Nasir al-Din al-Tusi and Abu Nasr Mansur. Al-Jayyani’s The book of unknown arcs of a sphere in the 11th century introduced the general  [ Read More ]

More than 4000 years ago, the Babyloneans and the Chinese already knew that a triangle with the sides of 3, 4 and 5 must be a right triangle. They used this knowledge to construct right angles. By dividing a string into twelve equal pieces and then laying it into a  [ Read More ]