Some quadratic equations cannot be solved by factorising and so an alternative method is the quadratic formula. It is based on a method called completing the square.

This tutorial shows you when to use it, clues that are given in a question and common mistakes that are often made.

How to solve a quadratic equation by the quadratic formula : ExamSolutions Maths Revision - youtube Video

How to Derive the Quadratic Formula

How to derive the Quadratic Formula : ExamSolutions Maths Revision - youtube Video