brackets anf factorisation 9th/10/2015

Factorise the expression: c²- 3c - 10

Write down the expression: 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 that:

• 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)