题目

命题∃x∈R，x2﹣x﹣1＜0的否定是（　　）                                            A．∃x∈R，x2﹣x﹣1≥0                                  B．∀x∈R，x2﹣x﹣1＜0          C．∀x∈R，x2﹣x﹣1＞0                                 D．∀x∈R，x2﹣x﹣1≥0           答案：D【分析】利用特称命题的否定是全称命题进行否定即可．                             【解答】解：根据全称命题的否定是特称命题得命题∃x∈R，x2﹣x﹣1＜0的否定是：∀x∈R，x2﹣x﹣1≥0                    故选：D．                                                                                          【点评】本题主要考查含有量词的命题的否定，要求熟练掌握特称命题的否定是全称命题，全称命题的否定是特称命题，比较基础．                                                                                         　                                                                                                      

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