Question

O是平面a上一点,点A\B\C所对的边是平面a上部贡献三点.平面a内的动点P满足向量OP=向量OA+b（向量AB+向量A

Answer 1

=1/2

OP= OA+1/2(AB+AC)

= OA+ 1/2(OB+OC-2OA)

= 1/2(OB+OC)

PA.(PB+PC)

=(OA-OP).(OB+OC-2OP)

=(OA- 1/2(OB+OC) ) .(OB+OC - (OB+OC) )

= 0