题目
双曲线的右焦点为，为双曲线上的一点，且位于第一象限，直线分别交于曲线于两点(点M在双曲线的左支上)，若为正三角形，则直线的斜率等于（） A． B． C． D．
答案：D【详解】记双曲线左焦点为，因为为正三角形，所以，即，，则有，，由双曲线定义可得：，设，，则，所以，两式作差可得，即，即，又，则 故选D
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