Triangle = dc, ch 2, dc. At the beginning of a row, 3ch stand in for the first stitch.

Ch 5, dc into first ch. (First triangle made.) Turn.

ch 5, dc into first dc, triangle into 3rch ch at end of row. Turn.

ch 5, dc into first dc, one triangle between every 2 triangles, triangle at end of row as before. Turn.

Keep going till you run out of yarn!