解:
(1)设A(x1,y1)B(x2,y2)
åæï¼y1=x1^2/(2p),y2=x2^2/(2p)
ç±äºCï¼y=x^2/(2p)
åï¼y'=x/p
åç¹Aå¤å线l1æçï¼k1=x1/p,
ç¹Bå¤å线l2æçï¼k2=x2/p
ç±äºï¼l1â¥l2
åï¼k1*k2=-1
å³ï¼x1x2=-p^2
ç±ï¼æç©çº¿Cå¨ç¹AãBå¤çå线åå«ä¸ºl1ãl2
ål1:x1*x=py+py1,l2:x2*x=py+py2
èç«l1,l2å¾ï¼
y=(x2y1-x1y2)/(x1-x2)
=[x2*x1^2/(2p)-x1*x2^2/(2p)]/(x1-x2)
=[(x1x2)(x1-x2)/2p]/(x1-x2)
=x1x2/(2p)
=-p/2
(2)ç±äºyD=-1
åï¼p=2
ç±äºï¼l1:x1*x=py+py1,l2:x2*x=py+py2
åï¼xD=p(y1-y2)/(x1-x2)
=(x1+x2)/2=3/2
åï¼x1+x2=3
åï¼x1x2=-p^2=-4
åï¼æ±å¾ï¼x1,x2æ å®æ ¹
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