ç¦ç¹å¨xè½´ä¸ï¼å¯è®¾æç©çº¿æ¹ç¨ä¸ºï¼y² = 2pxãå¯ä»¥å¤æç¦ç¹å¨(p/2,0)ç¹ã 设Aç¹åæ (x1,y1),Bç¹åæ (x2,y2)ï¼è®¾ABæçæ¯kï¼çº¿æ®µABçåç´å¹³å线æçæ¯k'
åï¼kk' = -1ï¼æ以ï¼
(y1-y2)/(x1-x2) * [(y1+y2)/2 - 0 ]/[(x1+x2)/2 - 6] = -1
(y1² - y2²) / [x1² - x2² -12(x1 - x2)] = -1
代å
¥y1²=2px1,y2²=2px2ï¼åç®ï¼
2p/(x1 + x2 - 12) = -1
x1 + x2 = 12 - 2p ---<1>
AF²=(x1 - p/2)² + y1² = (x1 - p/2)² + 2px1 = (x1 + p/2)²
AF = x1 + p/2
åçï¼
BF = x2 + p/2
AF + BF = x1 + x2 + p ---<2>
èç«<1>å<2>:
12 - 2p + p = 8
p=4
综ä¸ï¼
æç©çº¿æ¹ç¨ï¼
y² = 8x
温馨提示:答案为网友推荐,仅供参考