. .IV, V .97,99,105 . :
1) (1;1;z1) (2;2;z2), 
{2-1;2-1;z2-z1}
2) 
{; ; z}, : | | = 
3) (1;1;z1) (2;2;z2), (;;z) : = ½(1+2); = ½(1+2); z= ½(z1+z2)
4) :
= | | | 
cos( ), cos α = 
5) , : = x1x2+12+z1z2
, . ( ) , .
, - , , .
(Δ, 
, ∩, ║,┴,<)
