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Khan Academy
Proof of Quadratic Formula, Polynomial and Rational Functions, Algebra II
Armed with their newfound (or refreshed) knowledge of the quadratic formula, viewers can now work with Sal to prove the formula - an essential skill that is often ignored in algebra. Once they learn how to both use and prove the...
Khan Academy
Khan Academy: The Quadratic Formula: Proof of Quadratic Formula
Demonstrates how to derive the quadratic formula from the standard form of a quadratic equation by completing the square.