I was a Chinese mathematician, living in the 200s in the Wei Kingdom.
In 263, I published a book with solutions to mathematical problems presented in the famous Chinese book of mathematics known as The Nine Chapters on the Mathematical Art.
In this book, I devised an approximation method (usually accredited to Archimedes) to estimate pi to be 3.141014....The Nine Chapters used the value 3 as pi, while Zhang Heng had previously estimated it to be the square root of 10.
I also introduced sophisticated numerical techniques now known as Gaussian elimination (to solve systems of linear equatiuons) and Cavalieri's principle (to find the volume of a cylinder)...but they got the credit.
I also wrote a separate appendix involving new mathematics (especially related to surveying) called The Sea Island Mathematical Manual.
I am known as the first mathematicians who left roots as expressions unevaluated, thereby providing more exact results instead of approximations.
Liu Hui (circa 200)