问题
选择题
已知半径为R的圆中一条弧所对的圆周角为60°，那么它所对的弦长为（ ）
|
答案
作直径AD，连接BD，
由圆周角定理得：∠C=∠D=60°，
∵AB是⊙O直径，
∴∠ABD=90°，
∴sin∠D=
，AB AD
∴AB=AD•sin60°=2R×
=3 2
R．3
故选C．
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已知半径为R的圆中一条弧所对的圆周角为60°，那么它所对的弦长为（ ）
|
作直径AD，连接BD，
由圆周角定理得：∠C=∠D=60°，
∵AB是⊙O直径，
∴∠ABD=90°，
∴sin∠D=
，AB AD
∴AB=AD•sin60°=2R×
=3 2
R．3
故选C．
| 完形填空。 | |||
| A Chinese student went to England to study by plane. His name was Sun. It is spelt S-U-N just 1 the word "sun", the sun in the sky, is spelt. England is a country with 2 weather.It is often cloudy and rainy,so the people there don't get much sunlight (阳光) in the year. When 3 Chinese student arrived at London Airport,a tall English policeman opened his 4 to check the visa (签证). The policeman was 5 to find the Chinese name "Sun" in the passport. He thought it was pronounced just 6 the English word "sun". So he said to the student, "I see your name is Sun. You are 7 here." The Chinese student felt surprised. So he asked the policeman, "Is there anything wrong with my passport or visa? Do I have to 8 to my country?" "What?" shouted the policeman. "No,we'll never let you go away." The Chinese student was worried by now. He thought he was going to be arrested (逮捕). He was sure 9 he had been in trouble. 10 he wondered whether he had broken the British (英国的) law. So he asked the policeman again, "What happened? What have I done?" It was then that the policeman began to 11 . He' said, "You don't know what you have done, Mr Sun? You 12 sunlight to England! So we don't want you to go away." | |||
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