直线方程为x=y+2y^2=2p(y+2)y^2-2py-4p=0y1+y2=2p,y1y2=-4p(y1+4)/(y2-y1)=(y2-y1)/(y2+4)(y1+4)(y2+4)=(y2-y1)^2y1y2+4(y1+y2)+16=(y1+y2)^2-4y1y2-4p+8p+16=4p^2+16pp^2+3p-4=0p=1或p=-4(舍)P=1　　　　能不能用参数方程解?我们老师让用参数方程解答。谢谢了！直线方程为:x=t-2,y=t-4(t-4)^2=2p(t-2)t^2-(2p+8)t+16+4p=0t1+t2=2p+8t1*t2=16+4p等比:t1*t2=(t1-t2)^216+4p=(2p+8)^2-4(16+4p)p^2+3p-4=0p=1或 p=-4(舍)