х_(M)=(x_(B)+x_(C))/2=7
y_(M)=(y_(B)+y_(C))/2=11/2
z_(M)=(z_(B)+z_(C))/2=-1
Находим координаты
vector{AB}=(8-4;2-(-2);3-5)=(4;4;-2)
vector{AM}=(7-4; (11/2)-(-2); -1-5)=(3;15/2;-6)
cos ∠ BAM=(vector{AB}*vector{AM})/(|vector{AB}|*|vector{AM}|)=
=54/(6*sqrt(405))=9/sqrt(405)=1/sqrt(5)
∠ BAM=arccos(1/sqrt(5))
б)