AB-AD=DB(3/2)DO=(1/2)(DB+DC)AB+1/2BC-3/2DO-AD =(AB-AD)+1/2BC-3/2DO=DB+1/2BC-(1/2)(DB+DC)=DB+1/2BC-1/2DB-1/2DC=DB+1/2BC+1/2CD+1/2BD=DB+1/2BD+1/2BD=0
