Factorising is the reverse of multiplying out brackets.
We put an expression into brackets by taking out the highest common factor (HCF) of each term in the expression.
To work out what goes inside the brackets, we divide each term by this HCF.
Factorise fully 10x - 15x².
The HCF of 10x and 15x² is 5x.
So we take 5x outside the brackets and divide each term by 5x to work out what goes inside the brackets.
The answer is 5x(2 - 3x)
(Check by multipling out the brackets again)