The rule of the distance between the two points (x1, y1) and (x2, y2) is

a.
A = (0, 2) and B = (0, 1)
Substitute (x1, y1) by (0, 2) and (x2, y2) by (0, 1) in the given rule above

The length of AB is 1
b.
A = (0, 10) and B = (24, 0)
Substitute (x1, y1) by (0, 10) and (x2, y2) by (24, 0)

The length of AB is 26
c.
A = (5, 25) and B = (-16, -1)
Substitute (x1, y1) by (5, 25) and (x2, y2) by (-16, -1)

The length of AB is square root 1117