vector{BC}=(2;2;-2}
vector{BA}*vector{BC}=(-1)*2+2*2+(-3)*(-2)=8
|vector{BA}|=sqrt((-1)^2+2^2+(-3)^2)=sqrt(14)
|vector{BC}|=sqrt((2^2+2^2+(-2)^2)=sqrt(12)=2sqrt(3)
cos(vector{BA},vector{BC})=(vector{BA}*vector{BC})/|vector{BA}|*|vector{BC}|=
=8/(sqrt(14)*2sqrt(3))=4sqrt(42)/42=2sqrt(42)/21≈0,6172134
О т в е т. cos(vector{BA},vector{BC})=2sqrt(42)/21;
(vector{BA},vector{BC})≈ 52 градусов