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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...
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.
Paul Dawkins
Paul's Online Notes: Algebra: Applications of Quadratic Equations
Detailed math tutorial features notes and examples that review applications involving solving a quadratic equation including distance/rate problems and work rate problems.
Purple Math
Purplemath: The Quadratic Formula Explained
An excellent discussion on solving quadratic formulas, accompanied by numerous examples.
Purple Math
Purplemath: Complex Numbers: Introduction
This website provides an in-depth lesson on complex numbers. You learn about simplifying, adding, and multiplying complex numbers by viewing example problems that are worked through step-by-step. Continue on to pages 2 and 3 which...
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.
Khan Academy
Khan Academy: Number of Solutions of Quadratic Equations
Analyze quadratic equations in order to determine how many different real number solutions they have. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video or receive hints.