⇒
cos ∠ (vector{a},vector{AB})=(vector{a}*vector{AB})/(|vector{a}|*|vector{AB}|)
пр_(vector{AB})vector{a}=|vector{a}|*cos∠ (vector{a},vector{AB})=
= |vector{a}|*(vector{a}*vector{AB})/(|vector{a}|*|vector{AB}|)=
=(vector{a}*vector{AB})/|vector{AB}|
vector{AB}=(x_(B)-x_(A);y_(B)-y_(A); z_(B)-z_(A))= (4;4;2)
|vector{AB}|=sqrt(4^2+4^2+2^2)=sqrt(36)=6
vector{a}*vector{AB}=1*4+2*4+3*2=18
пр_(vector{AB})vector{a}=18/6=3
О т в е т. 3