AB
Write the coordinates in the boxes.  Then press 

xA = yA = zA =
xB = yB = zB =

d(A,B) =

xM =    yM =    zM =

d(A,B)^2 =

line AB:  x = xA+(xB-xA)*t, y = yA+(yB-yA)*t, z = zA+(zB-zA)*t

If you have to put a coefficient using some function symbol (1/5,π,√2,...), put it in a numerical form (calcolatrice) esempi