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This is a common song that recites the Quadratic Form, so the students can remember the complex formula.
2 Direct Instruction
Khan Academy is a great way a substitute teacher can present the lesson to the class. This link leads to a short lesson with concrete examples.
3 Guided Practice
In groups of two or three students can use this app to practice the Quadratic Formula. The teacher can still guide the students through the process and clarify any questions.
4 Independent Practice
Homework where the teacher can see relevant data and the students can use a finite number of hints.