Factorise x^2 - x - 6

You need 2 numbers that multiply together to make -6, and add together to make -1. The options to multiply to make -6 are: 6 and -1, -6 and 1, -3 and 2, 3 and -2. Looking at this list, the pair of numbers that add together to make -1 are -3 and 2. Therefore you can make the set of brackets as (x - 3)(x + 2). This answer can be checked by multiplying out the brackets again, and seeing if you get x² - x - 6.