World History Encyclopedia
World History Encyclopedia: Greek Mathematics
Discusses the major cultural influences on the development of mathematics in ancient Greece, and how the Greeks went on to surpass those cultures. The work of the Pythagoreans and of Euclid are described, along with some famous...
Wikimedia
Wikipedia: Irrational Number
At this site from Wikipedia you can learn the definition of an irrational number, then look at examples and explanations of why some numbers are irrational and others are not.