题目

已知正三角形的边心距为1，则这个三角形的面积为（ ） A．6 B．4 C．3 D．2 答案：C【考点】正多边形和圆． 【分析】作AD⊥BC与D，连接OB，则AD经过圆心O，∠ODB=90°，OD=1，由等边三角形的性质得出BD=CD，∠OBD=∠ABC=30°，得出OA=OB=2OD，求出AD、BC，△ABC的面积=BC•AD，即可得出结果． 【解答】解：如图所示： 作AD⊥BC与D，连接OB， 则AD经过圆心O，∠ODB=90°，OD=1， ∵△ABC是等边三角形， 听下面5段对话。每段对话后有一个小题，从题中所给的A、B、C三个选项中选出最佳选项，并标在试卷的相应位置。听完每段对话后，你都有10秒钟的时间来回答有关小题和阅读下一小题。每段对话仅读一遍。 1. What is the man's problem? A. He can't see clearly. B. He can't hear clearly. C. He doesn't know the answer. 2. What will the man do with the old house? A. Make it a hotel. B. Sell it. C. Rent it out. 3. How does the man like the singing performance of the Happy Girls? A. Boring. B. Wonderful. C. Just so-so. 4. What does the woman mean? A. She slept very well last night. B. She woke up once last night. C. She was woken up by a baby. 5. Where does the man want to go? A. To the lake. B. To the park. C. To the zoo.