how to find the length of the diagonal AB: steps.

1. Identify the coordinates of points A and B on a coordinate plane.

2. Use the distance formula to find the distance between points A and B. The distance formula is:
d = √((x2 - x1)^2 + (y2 - y1)^2)
where (x1, y1) and (x2, y2) are the coordinates of points A and B respectively.
3. Plug in the coordinates of points A and B into the distance formula to find the distance between them.
4. The result is the length of the diagonal AB.