2. count all rectangles of positive area formed by segments in a grid of m horizontal lines and n vertical lines.

Step-by-step explanation:

We have the grid has m horizontal lines and n vertical lines

We have to find the number of rectangles

If the grid is 1×1, there is 1 rectangle.

If the grid is 2×1, there will be 2 + 1 = 3 rectangles

If it grid is 3×1, there will be 3 + 2 + 1 = 6 rectangles.

So is there is there will be

If we add one column to firstly we will have as many rectangles in the 2nd column as the first,

And then we have that same number of rectangles.

So for rectanglesAfter solving  this we can say

For we have rectangles.

it’s the first one your welcome