Question

如图2-3-9,AB是⊙O的直径,BC是⊙O的切线,AC交⊙O于D,AB=6,BC=8,则BD等于(    )

图2-3-9

A.4               B.4.8                 C.5.2             D.6

Answer 1

解析:∵BC切圆于B,∴AB⊥BC.

∴∠ABC=90°.∴AC==10.

∵AB是⊙O直径,∴∠BDA=90°.∴∠ABC=∠ADB.

又∠A=∠A,∴△ABD∽△ACB.

∴=.

∴BD==4.8.

答案:B