Instructional Video7:44
Khan Academy

Proof of Quadratic Formula, Polynomial and Rational Functions, Algebra II

8th - 11th
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...
Instructional Video
Khan Academy

Khan Academy: The Quadratic Formula: Proof of Quadratic Formula

9th - 10th Standards
Demonstrates how to derive the quadratic formula from the standard form of a quadratic equation by completing the square.