If a quadratic equation factorises then we can solve it by using a factorising method as shown in this video.
In this tutorial you are shown how to solve a quadratic equation by using the method of completing the square. This is often used when a quadratic equation does not factorise.
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.