The number of different sets of three points of this 3-by-3 grid that can be the three vertices of an isosceles triangle is 8. The 8 sets of three points are: (1,1), (3,1), (3,3); (1,1), (3,1), (1,3); (1,1), (1,3), (3,3); (1,3), (3,1), (3,3); (1,1), (2,2), (3,1); (1,1), (2,2), (1,3); (2,2), (3,1), (1,3); (2,2), (3,1), (3,3).