搜题请搜索小程序“爱下问搜题”
问题 填空题

直线l经过抛物线y2=4x的焦点F，与抛物线交于A，B两点，则弦AB中点的轨迹方程为______．

答案

由题知抛物线焦点为（1，0）

当直线的斜率存在时，设为k，则焦点弦方程为y=k（x-1）

代入抛物线方程得所以k2x2-（2k2+4）x+k2=0，由题意知斜率不等于0，

方程是一个一元二次方程，由韦达定理：

x1+x2=

2k2+4
k2

所以中点横坐标：x=

x1+x2
2
=
k2+2
k2

代入直线方程

中点纵坐标：

y=k（x-1）=

2
k
．即中点为（
k2+2
k2
，
2
k
）

消参数k，得其方程为

y2=2x-2

当直线斜率不存在时，直线的中点是（1，0），符合题意，

故答案为：y2=2x-2

阅读理解

读短文，判断正(T)误(F)。

Dear mother,

     How are you? I'm fine.

     Today is Sunday. I don't go to school. I stay at home. I am writing to you now. Every day I go to

school at seven thirty in the morning. We have four classes in the morning. We read and write Chinese at

school. There are forty-five students in my class. Four of them are from the U. S. and five from Australia.

The other students are Chinese. Now I have many Chinese friends. My classmates are all my friends. They

teach me Chinese and I teach them English. I can speak a little Chinese now. Please don't worry about me.

                                                                                                                                    Yours,

                                                                                                                                         Jenny

(     ) 1. Jenny's mother writes the letter.

( ) 2. Every day Jenny has four classes.

( ) 3. Jenny can speak Chinese well.

( ) 4. There are forty-five students in Jenny's class.

( ) 5. Four of Jenny's classmates are from Australia.
查看答案
单项选择题

下列有关投标文件的送达内容的说法错误的是( )。

A．投标人应当在招标文件要求提交投标文件的时间前，将投标文件密封送达投标地点

B．投标人在招标文件要求提交投标文件的截止时间前，可以补充、修改或者撤回已提交的投标文件

C．在提交投标文件截止时间后到招标文件规定的投标有效期终止之前，投标人撤回投标文件的，其投标保证金将被没收

D．投标人在招标文件要求提交投标文件的截止时间前，补充、修改已提交投标文件的内容不能作为投标文件的组成部分
查看答案