The comments on the left explain it (I didn't understand it either). Basically, it's known that an equilateral triangle of side length n needs n^2 unit triangle

The comments on the left explain it (I didn't understand it either). Basically, it's known that an equilateral triangle of side length n needs n^2 unit triangles to perfectly tile it (e.g. you need 16 unit triangles to tile an equilateral triangle of side length 4). Now, if you make the side length of the large triangle just a teeny bit longer (that's what epsilon is), what is the minimum number of unit length triangles it takes to cover the larger triangle? The two different figures show two ways this can be done with n^2 + 2 triangles: the first figure essentially adds 2 triangles to the base row (the comments show how they overlap a little bit), while the second figure uses 3 overlapping triangles to make up the "tip", instead of just 1 (again, the comments show how this works because the base row doesn't need any additional triangles). Thus, these two examples show how it can be done with n^2 + 2 triangles. It's still an open question if it can be done with n^2 + 1.