题目

已知数列的相邻两项是关于的方程的两实根，且    （Ⅰ）求证：数列是等比数列；    （Ⅱ）是数列的前项的和．问是否存在常数，使得对都成立，若存在，求出的取值范围，若不存在，请说明理由． 答案：解：（Ⅰ）证明：是关于的方程的两实根，           ……2分               故数列是首项为，公比为-1的等比数列．……4分   （Ⅱ）由（Ⅰ）得，即                ……8分 因此，        要使，对都成立，        即（*） ……10分        ①当为正奇数时，由（*）式得：   �词汇运用 根据句意、首字母及汉语提示写出正确的单词（每小题1分，满分15分）1.No one can p _______ Jack from joining the society.2.Zhalong is a p????? ? place for many plants and animals3.Aunt Li is _______ (friend) to us.4.Do you have anything e _______?5.The government will p________ food and drink for the wild animals. 6.People may die w________ water and air? 7.You’d better _______ (not be) late for school again.8.Thanks for your _______ (invite).9.________ ( luck ),they ran away from the burning building with the help of firemen.10.Can you give me some __________（建议) on my English study?11.The local____________( 政府 )should take actions to protect the environment at once.12.It is necessary for everyone to know the ______________( 重要 ) of wetlands.13.Every year, lots of _______ (旅行者) go to the small town to enjoy the wonderful view.14.If people do nothing to protect them? , there will be __________ (一个没有) left.15.Finally ,the heavy rain? ???????? (导致)to a flood.