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You can also factorise quadratic equations. Remember that factorising an equation simplifies it in some way. Factorising is the reverse of expanding brackets.
Factorising quadratic equations
To factorise an equation such x2 + 5x + 6, you need to look for two numbers which 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) = x2 + 5x + 6
Factorising expressions gets trickier with negative numbers.
- Question
Factorise the expression c2- 3c - 10
- Answer
- Write down the equation:
- c2- 3c - 10
- Remember that to factorise an expression we need to look for common factor pairs.
- In this example we are looking for two numbers which:
- multiply to give -10
- add to give -3
- Think of all the factor pairs of -10:
- 1 and -10, -1 and 10, 2 and -5, -2 and 5
Which of these factor pairs can be added to get -3?
- Only 2 + (-5) = -3
So the answer is:
c2 - 3c - 10 = (c + 2)(c - 5)
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