I'll give this one a shot......but....I'm not overly confident.....!!!
Notice the follwing patterns......
For a 1 x 1 square, we have two possible values fo x and y, 0 and 1. And we have two ways to pick an apex point and a base of 1. But, we can orient these two triangles in 4 ways......apex points at the "top," apex points to the "right," apeax points to the "left" and apex points on the "bottom"....and each will have a base of 1...so that's eight possible triangles
1x 1 = (2 apex points)*(1 base) * [4 orientations] = 8 possible triangles
For a 2 x 2 square, we have three possible values for x and y .... 0, 1, 2. And we have three possible apex points, three possible bases - two of one unit and one of two units, and three possible heights - two of one unit and one of two units. And these can be oriented in 4 different ways, as before.
So the possible triangles in a 2 x 2 configuration are....
2 x 2 = [3 apex points]*[3 possible bases]* [3 possible heights]* [4 possible orientations] = 108 possible triangles
And for our situation, we have a 3 x 3 square.
We have four possible values for x and y - 0,1,2,3. And we have four possible apex points, 6 possible bases and heights- three of one unit, two of two units and three of one unit.... and four possible orientations, as before.
So....the possible triangles are
3 x 3 = [4 apex points]* [6 bases] *[6 heights]*[4 possible orientations ] = 576 possible triangles
It appears that the pattern for an n x n arrangement is [n + 1]*[C(n+1, 2)]^2 * 4
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I hope this is correct........can somebody else check my reasoning ????
