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问题: 平面向量

直角坐标平面xoy中,若定点A(1.2)与动点P(x,y)满足OA*OP+AP*OA=4(OA,OP,AP全是向量)则点P的轨迹方程是_________

解答:

A(1,2),P(x,y)
OA=i+2j, OP=xi+yj, AP=(x-1)i+(y-2)j
4 = OA*OP+AP*OA=(i+2j)(xi+yj)+[(x-1)i+(y-2)j](i+2j)
= (i+2j)[(2x-1)i+(2y-2)j]
= (2x-1)+2*(2y-2)
==> 2x+4y-9=0 <=== 点P的轨迹方程