Multiplying a number by itself (e.g. $ 6 \times 6$, or $6^2 $) is relatively easy. Going back the other way - finding out what number has been squared to get a particular result (or finding the "square root", e.g. $ \sqrt{36} $) - is tougher: you need to either just know the answer or just guess it (and, of course, square it to see if you were right, and then if you're wrong have another guess, informed by the outcome of your first one).
