This is a PDF presentation of deriving the quadratic formula. I have it set up in 29 slides. Print the 1st slide for the students.
Green and blue slides provide algebraic simplifications that are critical.
Yellow slides are for students to guess the next step.
The 1 red slide emphasizes the +- symbol.
This unravels a difficult concept as you go. The students fill in the proof 1 step at a time.