What is this golden ratio thing, anyway? It’s the number that is a solution for the equation (a + b)/a = (a/b). In other words, given a rectangle where the ratio of the length of its sides is 1:φ, when you remove the largest possible square from it, you’ll get another rectangle whose sides have the ratio φ:1. If you take the largest square from that, you’ll get a rectangle whose sides have the ratio 1:φ. And so on. You can see an image of the basic idea in Figure 3, The golden ratio.