单选题 In the figure below, equilateral triangle ABC is inscribed in circle O, whose radius is 4. Altitude BD is extended until it intersects the circle at E. What is the length of DE?

【正确答案】 C

【答案解析】Use TACTIC 5: to get DE, subtract OD from radius OE, which is 4. Draw AO (TACTIC 4). Since △AOD is a 30-60-90 right triangle, OD is 2 (one half of OA). So, DE = 4 - 2 = 2.
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