(本小题满分13分) 如图,双曲线的中心在坐标原点O,焦点在x轴上,两条渐近线分别为l1,l2,经过右焦点F垂直于l1的直线分别交l1,l2于A,B两点.又已知该双曲线的离心率. (1)求证:,,依次成等差数列; (2)若F(,0),求直线AB在双曲线上所截得的弦CD的长度. 答案:解:(1)由已知e2=,即=,故a2=c2, ① 从而b2=c2-a2=c2, ② 故==,设∠AOF=∠BOF=,=. 故tan∠AOB=tan2==,即=. 令=3m(m>0) ,则=4m,=5m,满足+=2, 所以,,,依次成等差数列. (2)由已知c2=5,
________ the flight to New York will be delayed is ________ I'm especially worried about.
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If; what
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Whether; that
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