Purple Math
Purplemath: Completing the Square: Deriving the Quadratic Formula
View examples on completing the square and deriving the quadratic formula. The key to solving by completing the square is "practice, practice, practice". By so doing, the process will become more "automatic", and you'll be much more...
National Council of Teachers of Mathematics
The Math Forum: Quadratic Formulas, Equations, Parabolas
Dr. Math here at the Math Forum, in a reply to a student question, helps find the vertex and coordinates of the parabola. The information is somewhat brief, but factual, and worth checking out.