Where does pi come from? Why should we be interested in negative numbers, or square roots of negative numbers? How did people ever figure out the quadratic formula? A truly wonderful reference for teachers at all levels.
This is the page illustrating the construction of an ellipse, from the Latin translation (1538) of the Treatise on Mensuration of Albrecht D�rer (1471-1528). This book was originally written in German and published in 1525 and was designed to teach German artists the geometrical ideas on which perspective in painting was based.