in the chessboard, There are 9 horizontal lines and 9 vertical lines. Choose two distinct horizontal lines, and two distinct vertical lines. (any rectangle determines a pair of horizontal lines and a pair of vertical lines)
so # rectangle = ^{9}C_{2} * ^{9}C_{2 }= 1296
u can see that there are 8^{2} small 1×1 squares, 7^{2} 2×2 squares, and so on down to 1^{2 }1×1 squares,,, u need to add to find total # squres
so # squres = 1^{2 }+ 2^{2} + 3^{2} + 4^{2 }+ 5^{2 }+ 6^{2 }+ 7^{2 }+ 8^{2 }= 204
number of rectangles in a chess board that are not sqaure = 1296 - 204 = 1092