由切线定理得PA=PB由切割线定理得,PA^2=PC*PD=PA*PB由弦切角定理,△PCB∽△PBD,故PB/PD=CB/BD,同理,△PCA∽△PAD,故PA/PD=CA/AD由△ECA∽△EBD得AC/BD=EC/EB由△EAD∽△ECB得BC/AD=EB/EDso,(PB/PD)*(PA/PD)=(PA*PB)/...