Factorising Quadratics

In this video we’re going to discover how to factorise quadratics. Quadratics are expressions with x2 as the highest power. Expanding and factorising are opposites. Factorising means to put into brackets, and with quadratics it is usually 2 brackets (x + 2)(x - 3). Each bracket is a factor. Let's factorise x2 + 3x - 10. Start by putting down your two brackets, both with an ‘x’ at the front: (x )(x ). Now look at the number that is on it's own at the end: -10. What multiplies to give negative 10? 2 and 5, or 1 and 10. Which combination of those add to give the number in the middle: + 3? +5, -2. So put these into the brackets. (x + 5)(x - 2). And that is the quadratic factorised. It is really important to check yourself, so quickly expand your answer to double check you’ve factorised correctly. Quadratics that start as x-squared, so with no number in front of the x2 are called monic quadratics. Quadratics that have a coefficient in front of the x-squared, like 3x2 are called non-monic quadratics. They are a little harder to factorise.