题目

若直线l1、l2的斜率分别是6x2＋x－1=0的两根，则l1与l2的夹角是A.15°                                                              B.30°C.45°                                                              D.60° 答案：解析:设直线l1、l2的斜率分别为k1、k2，由韦达定理知k1＋k2=－，k1·k2=－，∴|k2－k1|==.∴l1与l2的夹角α的正切值tanα=||==1.又α∈(0°，90°］，∴α=45°.答案:C

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