AE=AO+OB+BC+﹙1/2﹚﹙CB+BO+OP﹚
=-a+b-a+﹙1/2﹚﹙a-b+c﹚
=﹙-3/2﹚a+﹙1/2﹚b+﹙1/2﹚c
=xa+yb+zc
(x,y,z)=(-3/2,1/2,1/2)
[题目,或者答案,至少有一个打错了!]