Pythagoras

Pythagoras(~570-500BC) was an ancient Greek philosopher and mathematician. He travelled a lot when he was young, and concentrated on studies of different knowledge areas after coming back to his home country. He moved to the South of Italy in his old age. There he founded a political, religious and acadamic community. He and his followers were called the Pythagoreans. The relation between three sides of a right-angled triangle, as stated in Pythagoras' theorm, had already been mentioned in the ancient Chinese book on astronomy, Chou pei suan ching 周脾算經 . The content relating to the theorm described events which happened about 500 years before the time of Pythagoras. It denoted the shorter leg of a right-angled triangle by 'kou' 勾, the longer leg by 'ku' 股, and the hypotenuse by 'husan' 弦. Therefore the Chinese call this theorem the Kou-ku theorm.


For the Pythagoras' theorm(Kou-ku theorm)
Eg:
Triangle ABC: if angle C=90 degrees, AB is the hypotenuse side
ABxAB = ACxAC + BCxBC