Any expression of the form cannot always be factorised as with simple quadratics, by finding factors of c. Instead there is a slightly more complicated procedure, best illustrated by an example:

Factorise 1. Take out any common factor. Every term in the above expression has a factor 3, so we may write the expression as 2. Multiply the coefficient of by the constant term: Find the two factors of this product which add to give the coefficient of which in this case is -1.

3. Rewrite the term in brackets using these two factors: 4. Take out common factors for each pair: 5. Factorise completely: Example

Factorise 1. Take out common factors: 2. Multiply the coefficient of by the constant term:F ind the two factors of this product which add to give the coefficient of which in this case is -7: -1 and -6.

3. Rewrite the term in brackets using these two factors: 4. Take out common factors for each pair: 5. Factorise completely: Differences of Squares

Any expression of the form can be factorised almost instantly: Example: Example: 