Look at these expressions:

y² - 36

x² - 121

49 - p²

These are called the difference of two squares. Both terms in these expressions are squared: y² and 36, x² and 121, 49 and p².

You should look out for square numbers (1, 4, 9, 16, 25, ...) and a subtraction sign (this is what 'difference' means).

To factorise, set up two brackets, one with a minus and one with a plus sign and square root the terms.

y² - 36 = (y - 6)(y + 6)

x² - 121 = (x - 11)(x + 11)

49 - 4p² = (7 - 2p)(7 + 2p)