CK-12 Foundation
Ck 12: Analysis: Quadratic Formula and Complex Sums
[Free Registration/Login may be required to access all resource tools.] This lesson covers solving quadratic equations when the answers are complex numbers. Students examine guided notes, review guided practice and attempt practice...
Math Planet
Math Planet: Completing the Square
If you've got a quadratic equation on the form of ax^2 + c = 0 Then you can solve the equation by using the square root of x = square_root(-c/a) or x = -square_root(-c/a)