neutronw
幼苗
共回答了11个问题采纳率:100% 举报
设A(x1,y1) B(x2,y2) M(x0,y0)
N(-p/2,y0) F(p/2,0)
点差法计算AB斜率:
A,B满足抛物线方程y1^2=2px1 y2^2=2px2
两式相减y1^2-y2^2=2px1-2px2
K(AB)=(y1-y2)/(x1-x2)=2p/(y1+y2)=p/y0
两点计算斜率K(NF)=(y0-0)/(-p/2-p/2)=-y0/p
K(AB)*K(NF)=-1 =>FN垂直于AB
1年前
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