Consider a triangle drawn on the X – Y plane with its three vertices at (41, 0), (0, 41) and (0, 0), each vertex being represented by its (X, Y) coordinates. The number of points with integer coordinates inside the triangle (excluding all the points on the boundary) is (CAT 2005)
The equation forming from the data is x + y < 41, as we cannot count the perimeter of the triangle.
Thus,total number of cases will fall in an AP with first term 39 with cd =1 and last term =1.
Thus number of coordinates =39×402=780