搜题请搜索小程序“爱下问搜题”
问题 填空题
椭圆
x2
4
+
y2
m
=1的离心率为
1
2
，则m=______．
答案

方程中4和m哪个大，哪个就是a2，

（ⅰ）若0＜m＜4，则a2=4，b2=m，

∴c=

4-m
，∴e=
4-m
2
=
1
2
，得 m=3；

（ⅱ）m＞4，则b2=4，a2=m，

∴c=

m-4
，∴e=
m-4
m
=
1
2
，得  m=
16
3
；

综上：m=3或m=

16
3
，

故答案为：3或

16
3
．

单项选择题

区分量变和质变的根本标志是（ ）

A．事物的变化是否显著

B．事物的变化是否迅速

C．事物的变化是否突破原有的度

D．事物的变化是否合乎规律
查看答案
单项选择题

Light utility trucks have become popular among consumers who buy them primarily for the trucks rugged appearance. Yet although, these trucks are tough-looking, they are exempt from the government’s car-safety standards that dictate minimum roof strength and minimum resistance to impact. Therefore, if involved in a serious high-impact accident, a driver of one of these trucks is more likely to be injured than is a driver of a car that is subject to these government standards.
The argument depends on the assumption that

A．the government has established safety standards for the construction of light utility trucks.

B．people who buy automobiles solely for their appearance are more likely than other people to drive recklessly.

C．light utility trucks are more likely than other kinds of vehicles to be involved in accidents that result in injuries.

D．the trucks’ rugged appearance is deceptive in that their engines are not especially powerful.

E．(E) light utility trucks are less likely to meet the car-safety standards than are cars that are subject to the standards.
查看答案