If you're only counting the smallest triangles, then 8.
If you're counting all possible triangles including triangles made of other triangles, then 16. Each diagonal gives 2, the combined diagonals give 4, and the unit triangles give 8 for a total of 2 + 2 + 4 + 8 = 16.
If we divide a square by it's 4 lines of symmetry, we can see that their are 8 single triangles, 4 double triangles, and 4 quadruple triangles. 8 + 4 + 4 = 16 There should be a total of 16 triangles. Hope this helps!
