We have an equilateral triangle of side . It's been cut into equilateral triangles of side 1 and some rhombi whose acute angles is . I have to show that . So, it's straightforward when I draw it, that there are less than pairs of different smaller triangles with one common side. I could describe the situation as I see it, which is trying to stick in another rhombus step-by-step to show when it eventually becomes impossible. But is there a more formal way to do that? If not, what's the most formal way of presenting what I have described?