Mine is not all that good. There is something I just realized and I am still having trouble seeing why it works.

Suppose you have an equilateral triangle that you want to divide into 9 smaller triangles, 1 on top, 3 in the next row, and 5 on the bottom row. Is it obvious what the simplest way of doing this is? It was not for me, and it only occurred to me after thinking about it.