å½Lâ¥xè½´æ¶
x1=x2=p/2
x1*x2=p^2/4
y1=p,y2=-p
y1*y2=-p^2
å½Lä¸åç´xè½´æ¶
设y=k(x-p/2)
代å
¥y^2=2px
å¾
k^2x^2-(pk^2+2p)x+k^2p^2/4=0
é¦è¾¾å®ç
x1x2=k^2p^2/4/k^2=p^2/4
y1y2
=k^2(x1x2-(x1+x2)*p/2+p^2/4)
=-p^2
x1x2,y1y2为å®å¼
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