回复：公布我的答案：只需做一条辅助线

This is a good problem.But I don't understand your prove.I think Euc. geometry is weak for this question.P(x.y),P'(a^2/c,y),Q(0,-b^2y/a^),A(-c,0),B(c,0)andC(b^2x/(a^2+b^2).We can prove AC*BC=PC*QC.It is easy but borring.We get the anwser.