题目

已知椭圆的离心率，且椭圆与圆的4个交点恰为一个正方形的4个顶点.（1）求椭圆的标准方程；（2）已知点为椭圆的下顶点， 为椭圆上与不重合的两点，若直线与直线的斜率之和为，试判断是否存在定点，使得直线恒过点，若存在，求出点的坐标；若不存在，请说明理由. 答案：【答案】(1) (2) 存在定点，使得直线恒过点【解析】试题分析：（1）第（1）问，直接根据已知条件得到关于a,b的一个方程组，再解方程组即可. (2)第（2）问，对直线的斜率分两种情况讨论.每一种情况都要先根据已知条件求直线DE的方程，再判断其方程是否过定点.试题解析：（1）因为椭圆的离心率，所 选出与所给句子画线部分意义相同或相近的选项。 1．If you have a fever，you should drink a lot of water． A．more              B．many              C．a great deal          D．lots of 2．When he was young，he had to look after his sick mother after school． A．looked for          B．took care of         C．took part in       D．looked to 3．We had fun at the birthday party． A．danced and sang                         B．enjoyed ourselves C，had delicious food                         D．did fun 4．Sorry，Mr. Wang isn't hi at the moment． A．at that moment       B．a moment ago       C．just now           D．right now 5．You don't have to finish your homework now． A．mustn't             B．needn't              C．can't              D．shouldn't