(1) AB⃗=b−a\vec{AB} = b - aAB=b−a (2) BC⃗=−a−b\vec{BC} = -a - bBC=−a−b (3) CD⃗=a−b\vec{CD} = a - bCD=a−b (4) BD⃗=−2b\vec{BD} = -2bBD=−2b