A line segment on a coordinate grid joins the point (2, 3) to the point (2, 9). How long is this segment?

Erklärung

Both ends share the same sideways value, so the segment runs straight up and its length is the gap from 3 to 9. Counting the grid lines it touches gives 7 because that counts both ends as well as the gaps between them, and it is the gaps that measure distance.