题目

双曲线=1的焦点到准线的距离是A.                                                               B.C.或                                                      D.或 答案：解析:∵a2=9,b2=7,∴c=4.∴双曲线的焦点坐标是(±4，0)，准线方程是x=±.∴双曲线的焦点到准线的距离为4－＝和4＋＝.答案:C

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