如图2-5-8PAB、PCD为⊙O的两条割线若PA=5AB=7CD=11则AC∶BD等于()图2-5-8A.1∶3B.5∶12C.5∶7D.5∶11

Question

如图2-5-8 PAB、PCD为⊙O的两条割线 若PA=5 AB=7 CD=11 则AC∶BD等于(    )

图2-5-8

A.1∶3             B.5∶12             C.5∶7             D.5∶11

Answer 1

解析:由割线定理得PA·PB=PC·PD

∴5×(5+7)=PC(PC+11).

∴PC=4或PC=-15(舍去).

又∵PA·PB=PC·PD ∠P=∠P

∴△PAC∽△PDB.

∴.

答案:A