How do we calculate distances?

Distance formula:

Ex:

Calculate the length of a segment whose endpoints are at (-1,5) and (7,3).

X_2= 2, X_{1= -1,} Y_{2= 3,} Y_1= 7

d= √(2--1)² + (3-7)²
d= √(9 + 16)
d= √25
d= 5

http://booknerd3.deviantart.com/art/Distance-Formula-208719112