Purple Math
Purplemath: Conics: Parabolas: Introduction
This reference material introduces the terms and equations related to parabolas in the context of conics. Also, relates concepts to previously-learned material and shows how to 'read' from the 'conics' form of the parabola equation.
University of Toronto (Canada)
University of Toronto Mathematics: Is There Really Such a Thing as "Infinity"?
See how the existence of infinity depends on the context in which it is used. Offers a look at the concept of infinity from different view points.