ï¼1ï¼AF1â¥AF2
å 为|F1F2|=2cï¼â AF1F2=60°ï¼æ以|AF1|=cï¼|AF2|=â3c.
ç±æ¤åå®ä¹ç¥|AF1|+|AF2|=2aï¼æ以2a=(â3+1)cï¼e=c/a=â3-1.
ï¼2ï¼è®¾A(x1,y1)ï¼B(x2,y2). F2(1,0)
设ç´çº¿ABæ¹ç¨ä¸ºy=k(x+1)ï¼ä¸x²+2y²=2èç«å¾(2k²+1)x²+4k²x+2k²-2=0
æ以x1+x2=-4k²/(2k²+1)ï¼x1x2=(2k²-2)/(2k²+1)ï¼y1y2=-k²/(2k²+1).
F2A·F2B=(x1-1,y1)·(x2-1,y2)=x1x2-(x1+x2)+1+y1y2=(7k²-1)/(2k²+1)
=7/2-9/(4k²+2).
æ以å½k=0æ¶ï¼ä¸å¼ææå°å¼-1.
kâ+âæ¶ï¼F2A·F2Bâ7/2.
温馨提示:答案为网友推荐,仅供参考