Liu Hui was a Chinese mathematician who lived in the 200s in the Wei Kingdom.
In 263 he published a book with solutions to mathematical problems presented in the famous Chinese book of mathematics known as Jiuzhang Suanshu or The Nine Chapters on the Mathematical Art.
In these commentaries he presented(among other things ):
An estimate of π in the comments to chapter 1. He estimated pi to 3. 141014 with a 192 sided polygon and later calculated pi as 3. 14159 by using a 3 079 sided polygon.
He suggested that 3. 14 was a good approximation.
His estimation is made with a method similar to Archimedes.
The Nine Chapters used the value 3 as π, but Zhang Heng had previously estimated it to the square root of 10;
Cavalieri's principle to find the volume of a cylinder.
He also presented, in a separate appendix called Haidao suanjing or The Sea Island Mathematical Manual, several problems related to surveying.
Liu was one of the first mathematicians known to leave roots unevaluated, giving more exact results instead of approximations.