(1)OM = (1/2)(OB+OD) = (1/2)(OA+AB + OA+AD)=(1/2)( 2(-1,2) + (4,3)+(-3,-1))= (1/2)(-1,6)(2)OB= OA+AB = (3,1)OD = OA+AD=(-4,-3)OP=(2,y)PB=λBDOB-OP = λ(OD-OB)(1,1-y) =...A(-1,-2)是-2不是2OM = (1/2)(OB+OD)= (1/2)(OA+AB + OA+AD)=(1/2)( 2(-1,-2) + (4,3)+(-3,-1))= (1/2)(-1,-2)我是这样算的：BD=AD-AB=(-3，-1)-(4，3)=(-7，-4)所以点M（-3.5，-2）能不能看一下哪里错了？BD = (-7,-4)M is mid point of BDOM = (OB+OD)/2 不等于 (1/2)BD