一道简单的中学几何题!如图,AB是⊙O的直径,∠BAC=60度,P是AB上一点,过P作AB的垂线与AC的延长线交与点Q,
8个回答

(1)由已知得∠ACB = 90,∠ABC = 30,

∴ ∠Q = 30,∠BCO = ∠ABC = 30.

∵ CD是⊙O的切线,CO是半径,

∴ CD⊥CO,

∴ ∠DCQ =∠BCO = 30,

∴ ∠DCQ =∠Q,故△CDQ是等腰三角形.

(2)设⊙O的半径为1,则AB = 2,OC = 1,AC = AB∕2 = 1,BC =根号3 .

∵ 等腰三角形CDQ与等腰三角形COB全等,∴ CQ = BC = 根号3.

于是 AQ = AC + CQ = 1 +根号3 ,进而 AP = AQ∕2 =(1 +根号3 )∕2,

∴ BP = AB-AP = 2-(1 +根号3 )∕2 =(3-根号3 )∕2,

PO = AP-AO =(1 +根号3 )∕2-1 =( 根号3-1)∕2,

∴ BP:PO =根号3.