This activity is about working out the difference of two square numbers.
We use the fact that a2 - b2 factorises to (a + b) (a - b)
Using this fact, we can work out:
152 - 82 = (15 + 8) × (15 - 8) = 23 × 7 = 161
Being able to find the difference between two squares in this way can sometimes make it possible to do the calculation without the use of a calculator!
Let's have a go at some questions.