½â´ð£º½â£º£¨1£©ÉèÅ×ÎïÏߵĽâÎöʽÊÇy=ax
2+bx+c£¬
¡ßÕý·½Ðεı߳¤2£¬
¡àBµÄ×ø±ê£¨2£¬-2£©AµãµÄ×ø±êÊÇ£¨0£¬-2£©£¬
°ÑA£¨0£¬-2£©£¬B£¨2£¬-2£©£¬D£¨4£¬-
£©´úÈëµÃ£º
£¬
½âµÃa=
£¬b=-
£¬c=-2£¬
¡àÅ×ÎïÏߵĽâÎöʽΪ£º
y=x2-x-2£¬
´ð£ºÅ×ÎïÏߵĽâÎöʽΪ£º
y=x2-x-2£®
£¨2£©¢ÙÓÉͼÏóÖª£ºPB=2-2t£¬BQ=t£¬
¡àS=PQ
2=PB
2+BQ
2£¬
=£¨2-2t£©
2+t
2£¬
¼´S=5t
2-8t+4£¨0¡Üt¡Ü1£©£®
´ð£ºSÓëÔ˶¯Ê±¼ätÖ®¼äµÄº¯Êý¹ØϵʽÊÇS=5t
2-8t+4£¬tµÄÈ¡Öµ·¶Î§ÊÇ0¡Üt¡Ü1£®
¢Ú½â£º¼ÙÉè´æÔÚµãR£¬¿É¹¹³ÉÒÔP¡¢B¡¢R¡¢QΪ¶¥µãµÄƽÐÐËıßÐΣ®
¡ßS=5t
2-8t+4£¨0¡Üt¡Ü1£©£¬
¡àµ±S=
ʱ£¬5t
2-8t+4=
£¬µÃ20t
2-32t+11=0£¬
½âµÃt=
£¬t=
£¨²»ºÏÌâÒ⣬ÉáÈ¥£©£¬
´ËʱµãPµÄ×ø±êΪ£¨1£¬-2£©£¬QµãµÄ×ø±êΪ£¨2£¬-
£©£¬
ÈôRµã´æÔÚ£¬·ÖÇé¿öÌÖÂÛ£º
£¨i£©¼ÙÉèRÔÚBQµÄÓұߣ¬Èçͼ£¨1£©Ëùʾ£¬ÕâʱQR=PB£¬RQ¡ÎPB£¬
ÔòRµÄºá×ø±êΪ3£¬RµÄ×Ý×ø±êΪ-
£¬
¼´R£¨3£¬-
£©£¬
´úÈë
y=x2-x-2£¬×óÓÒÁ½±ßÏàµÈ£¬
¡àÕâʱ´æÔÚR£¨3£¬-
£©Âú×ãÌâÒ⣻
£¨ii£©¼ÙÉèRÔÚQBµÄ×ó±ßʱ£¬ÕâʱPR=QB£¬PR¡ÎQB£¬
ÔòR£¨1£¬-
£©´úÈ룬
y=x2-x-2£¬
×óÓÒ²»ÏàµÈ£¬¡àR²»ÔÚÅ×ÎïÏßÉÏ£®
×ÛÉÏËùÊö£¬´æÔÚÒ»µãR£¨3£¬-
£©Âú×ãÌâÒ⣮
![¾«Ó¢¼Ò½ÌÍø](http://thumb.1010pic.com/pic3/upload/images/201406/54/3d2dc59f.png)
Ôò´æÔÚ£¬RµãµÄ×ø±êÊÇ£¨3£¬-
£©£»
£¨3£©Èçͼ£¨2£©£¬M¡äB=M¡äA£¬
¡ßA¹ØÓÚÅ×ÎïÏߵĶԳÆÖáµÄ¶Ô³ÆµãΪB£¬¹ýB¡¢DµÄÖ±ÏßÓëÅ×ÎïÏߵĶԳÆÖáµÄ½»µãΪËùÇóM£¬
ÀíÓÉÊÇ£º¡ßMA=MB£¬ÈôM²»ÎªLÓëDBµÄ½»µã£¬ÔòÈýµãB¡¢M¡¢D¹¹³ÉÈý½ÇÐΣ¬
¡à|MD|-|MB|£¼|DB|£¬
¼´Mµ½D¡¢AµÄ¾àÀëÖ®²îΪ|DB|ʱ£¬²îÖµ×î´ó£¬
![¾«Ó¢¼Ò½ÌÍø](http://thumb.1010pic.com/pic3/upload/images/201406/54/f7a58531.png)
ÉèÖ±ÏßBDµÄ½âÎöʽÊÇy=kx+b£¬°ÑB¡¢DµÄ×ø±ê´úÈëµÃ£º
£¬
½âµÃ£ºk=
£¬b=-
£¬
¡ày=
x-
£¬
Å×ÎïÏß
y=x2-x-2µÄ¶Ô³ÆÖáÊÇx=1£¬
°Ñx=1´úÈëµÃ£ºy=-
¡àMµÄ×ø±êΪ£¨1£¬-
£©£»
´ð£ºMµÄ×ø±êΪ£¨1£¬-
£©£®