A2A: This is more a math question than a chess question since the chessboard here is a proxy for a coordinate plane. As a result, I may not be the most qualified to answer it, but I think I've got a grip on the right answer. read more
Well there are 9 total. So 9c2. Order doesn't matter, which is why we use combinations . This equals 36. How many ways can you choose two horizontal lines. There are 9c2. Again order doesn't matter, so we use combinations. It equals 36 again. read more