To derive the quadratic formula, the method that must be used is completing the square. This technique is essential for transforming the general quadratic equation $ax^2 + bx + c = 0$ into a form that allows the quadratic formula to be extracted.

Would you like more details on how completing the square leads to the quadratic formula?

Here are 5 follow-up questions to consider:

1. What is the general form of a quadratic equation?
2. How is the process of completing the square done step-by-step?
3. What are the key advantages of using the quadratic formula over other methods?
4. Can the quadratic formula be derived using any other methods?
5. What are some real-world applications of the quadratic formula?

Tip: When solving quadratic equations, always check if factoring is possible before applying the quadratic formula—it can save time!