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Khan Academy
Khan Academy: Algebra: Complex Numbers: Complex Roots From the Quadratic Formula
Video shows how to use the quadratic formula to find roots of a quadratic equation in a situation where the roots are complex. Includes showing how to verify the answers are correct solutions of the quadratic. [10:15]
Randy Thomas
Solving Quadratic Equations With Complex Solutions
This tutorial discusses solving quadratic equations using square roots, completing the square, and the quadratic formula. Problems which previously had no solution can now be solved with the inclusion of the complex number system....