Paul Dawkins
Paul's Online Notes: Algebra: Quadratic Equations Part Ii
Detailed math tutorial features notes and examples that illustrate how to solve quadratic equations using complete the square then use that to derive the quadratic formula.
Texas Education Agency
Texas Gateway: Solving Quadratic Equations Using Algebraic Methods
Given a quadratic equation, the student will solve the equation by factoring, completing the square, or by using the quadratic formula.
Other
Dans Math: Lessons: Intermediate Algebra
College professor Dan Bach presents a review of algebra concepts, including factoring, quadratic equations, and graphing parabolas. The examples are detailed, but easy to follow. This is a good site for reviewing before tests and quizzes.
CK-12 Foundation
Ck 12: Algebra: Vertex Form of a Quadratic Equation
[Free Registration/Login may be required to access all resource tools.] Write quadratic functions in vertex form and find their vertex and intercepts.