Seek the detailed answer flow of the eighth multiple-choice question in mathematics of 20 10 Suihua senior high school entrance examination! ! !
Connect CD from the theorem: ∠D=∠B, so sinD=sinB= 1/3. ∠DCA=90 degrees, so AC/AD= 1/3. Because the radius of circle O is 6 and the diameter is 12, 12* 1/3=4, so choose B.