A(x1,y1),B(x2,y2)
x^2=2py,y=kx+2
x^2-2pkx-4p=0
x1+x2=2pk, x1x2=4p
向量OA=(x1,y1) 向量OB=(x2,y2)
向量OA*向量OB=x1x2+y1y2=2
y1y2=(kx1+2)(kx2+2)=k^2x1x2+2k(x1+x2)+4=4pk^2+4pk^2+4=8pk^2+4
2pk+8pk^2+4=2
4pk^2+pk+1=0
A(x1,y1),B(x2,y2)
x^2=2py,y=kx+2
x^2-2pkx-4p=0
x1+x2=2pk, x1x2=4p
向量OA=(x1,y1) 向量OB=(x2,y2)
向量OA*向量OB=x1x2+y1y2=2
y1y2=(kx1+2)(kx2+2)=k^2x1x2+2k(x1+x2)+4=4pk^2+4pk^2+4=8pk^2+4
2pk+8pk^2+4=2
4pk^2+pk+1=0