vector{BK}= vector{AC} = vector{a}
По правилу треугольника
vector{DK}= vector{BK} - vector{BD}= vector{a} - vector{b}
vector{AB}=(1/2)vector{DK}= (vector{a} - vector{b})/2
vector{CD}=-vector{AB}
vector{CD}=(vector{b} - vector{a})/2
Переносим вектор vector{AC} в точку D ( cм. рис.2), получаем
vector{DP}= vector{AC} = vector{a}
По правилу треугольника
vector{BP}= vector{BD} + vector{BP}= vector{b} + vector{a}
vector{BC}=(1/2)vector{BP}= (vector{a} + vector{b})/2
vector{DA}=-vector{BC}
vector{DA}=(-vector{a} - vector{b})/2
О т в е т.
vector{AB}= (vector{a} - vector{b})/2
vector{CD}=(vector{b} - vector{a})/2
vector{BC}= (vector{a} + vector{b})/2
vector{DA}=(-vector{a} - vector{b})/2