1.设M(-1,a),N(-1,b),P(x,y)FM=(-2,a),FN=(-2,b),MP=(x+1,y+a),OP=(x,y),OF=(1,0),NO=(1,-b)由题意4+ab=0y+a=0,x/1=y/-by=-a,x=a/b即y2=4x2.设L的斜率为k,则L:y=k(x-1),代入y2=4x得k2x2-(2k2+4)x+k2=0设A(x1,y1),B(x2,y2)则x1x2=1,y12=4x1,y22=4x2y1y2=-4(y1,y2异号)向量OA点乘向量OB=x1x2+y1y2=1-4=-3 |