precal
posted by ladybug .
find the distance d (P1 P2) between the P1 and P2
P1=(1,1);P2=(1,2)

d = sqrt [ ( x2  x1 ) ^ 2 + ( y2  y1 ) ^ 2 ]
In this case :
x1 =  1
y1 = 1
x2 = 1
y2 = 2
d = sqrt [ ( 1  (  1 ) ) ^ 2 + ( 2  1 ) ^ 2 ]
d = sqrt [ ( 1 + 1 ) ) ^ 2 + 1 ^ 2 ]
d = sqrt [ 2 ^ 2 + 1 ]
d = sqrt ( 4 + 1 )
d = sqrt ( 5 )