Purple Math
Purplemath: Completing the Square: Deriving the Vertex Formula
This resource describes in steps how to derive the vertex formula.
Lawrence Hall of Science
The Math Page: Topics in Pre Calculus: Completing the Square
Here is a site that clearly and thoroughly explains how to solve quadratic equations by completing the square. The quadratic formula is derived using this method on this page. Point this site out to students who have been absent or who...
Other
Center for Technology and Teacher Education: Parabola Lesson Plan
This site is a lesson plan on construction of a parabola using the definition. Geometer's Sketch Pad software is beneficial for the activity. Through the activity students develop gemetric constructions of parabolas, use the distance...