Socrates devotes an entire dialogue, Meno, to the doubling of the area of the square. It is one of his most patronising and could have been much improved (and reduced) by a few lines drawn in the sand. But if it has to be in words then you double a square by drawing a new square based on the diagonal of the first. I prefer lines in the sand or, even better, a sumptuous art print. Best of all, an entire wall - maybe yours...