一道有关圆的证明题(比例线段)
来源:学生作业帮 编辑:搜狗做题网作业帮 分类:数学作业 时间:2024/08/13 08:57:39
一道有关圆的证明题(比例线段)
过圆外一点P引这个圆的两条切线PA和PB分别切圆与A和B,连接AB,点M是圆上一动点,连接PM交圆于N,交AB与Q.(M在N左侧)
证明:PM/PN=QM/QN
有点难度!
![](http://img.wesiedu.com/upload/6/00/600e78a510049c1eb8c8b7edba8a8214.jpg)
过圆外一点P引这个圆的两条切线PA和PB分别切圆与A和B,连接AB,点M是圆上一动点,连接PM交圆于N,交AB与Q.(M在N左侧)
证明:PM/PN=QM/QN
有点难度!
![](http://img.wesiedu.com/upload/6/00/600e78a510049c1eb8c8b7edba8a8214.jpg)
![一道有关圆的证明题(比例线段)](/uploads/image/z/18138941-53-1.jpg?t=%E4%B8%80%E9%81%93%E6%9C%89%E5%85%B3%E5%9C%86%E7%9A%84%E8%AF%81%E6%98%8E%E9%A2%98%EF%BC%88%E6%AF%94%E4%BE%8B%E7%BA%BF%E6%AE%B5%EF%BC%89)
⊿PAN∽⊿PMA => AN/AM=PA/PM ...(1)
⊿PBN∽⊿PMB => BN/BM=PB/PM ...(2)
(1)*(2):
PA^2/PM^2=PM*PN/PM^2=PN/PM=(AN/AM)*(BN/BM)=(AN/BM)*(BN/AM) ...(3)
⊿AQN∽⊿MQB => AN/BM=QN/QB ...(4)
⊿AMQ∽⊿NBQ => BN/AM=QN/QA ...(5)
(4)*(5):
(AN/BM)*(BN/AM)=QN^2/(QA*QB)=QN^2/(QN*QM)=QN/QM ...(6)
(3),(6)立得:
PN/PM=QN/QM
得证
⊿PBN∽⊿PMB => BN/BM=PB/PM ...(2)
(1)*(2):
PA^2/PM^2=PM*PN/PM^2=PN/PM=(AN/AM)*(BN/BM)=(AN/BM)*(BN/AM) ...(3)
⊿AQN∽⊿MQB => AN/BM=QN/QB ...(4)
⊿AMQ∽⊿NBQ => BN/AM=QN/QA ...(5)
(4)*(5):
(AN/BM)*(BN/AM)=QN^2/(QA*QB)=QN^2/(QN*QM)=QN/QM ...(6)
(3),(6)立得:
PN/PM=QN/QM
得证