如题所述
å¦å¾ï¼AD为â³ABCçè§å¹³å线ï¼è¿ç¹Dåè¾¹AB,ACåå«å¼å线DE,DF.åDE=DF.
Sâ³ABDï¼Sâ³ACD=BD/CD
åå 为Sâ³ABDï¼Sâ³ACD=ï¼ABÃDEï¼ï¼ï¼ACÃDFï¼=ABï¼AC
æ以BD/CD=AB/AC.
æçé®æ¬¢è¿è¿½é®ï¼ï¼ï¼