How would you do practise test 3, section 3, question 16? I plugged in 1 and happened to get the answer. But is there an algebraic way to do it?

Thanks!

Sure. Algebraically, you can do it in a few steps:

You can actually go further by expanding the differences of two squares if you want (below), but because the question tells you that , you know from the above that it can either be 1 or 2.