# Quadratic equations

**Multiply these brackets to remind yourself how to factorise.**

**( x + 2 ) ( x + 5 ) = x**^{2}+ 7x + 10**( x + 2 ) ( x + 3 ) = x**^{2}+ 5x + 6**( x - 3 ) ( x - 5 ) = x**^{2}- 8x + 15**( x + 6 ) ( x - 5 ) = x**^{2}+ x - 30**( x - 6 ) ( x + 5 ) = x**^{2}- x - 30

**To factorise an expression such x ^{2} + 5x + 6, you need to look for two numbers that add up to make 5 and multiply to give 6.**

**The factor pairs of 6 are:**

**1 and 6****2 and 3**

**2 and 3 add up to 5. So: (x +2) (x+3) = x ^{2} + 5x + 6**

**Factorising expressions gets trickier with negative numbers.**

**Some quadratic expressions have only a term in x ^{2} and a number such as x^{2} - 25.**

**These quadratic expressions have no x term.**

**Using our method to factorise quadratics means we look for two numbers that multiply to make -25 and add to make 0.**

**The only factor pair that will work are 5 and -5. So:**

**(x + 5)(x – 5) = x² - 25**

**Not all quadratic expressions without an x term can be factorised.**

- Created by: Tayloe35
- Created on: 26-09-14 10:46

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