搜题请搜索小程序“爱下问搜题”
问题 选择题
在△ABC中，a，b，c分别是∠A，∠B，∠C所对应的边，∠C=90°，则
a+b
c
的取值范围是（　　）
A．（1，2）B．(1，
2
)		C．(1，
2
]		D．[1，
2
]
答案

由正弦定理得：

a
sinA
=
b
sinB
=
c
sinC
，又sinC=1，

∴a=csinA，b=csinB，

所以

a+b
c
=
csinA+csinB
c
，由A+B=90°，得到sinB=cosA，

则

csinA+csinB
c
=sinA+sinB=sinA+cosA=
2
sin（A+
π
4
），

∵∠C=

π
2
∴A∈（0，
π
2
），∴sin（A+
π
4
）∈（
2
2
，1]，

∴

a+b
c
∈（1，
2
]．

故选C．

单项选择题

井点施工工艺程序为( )。

A．放线定位→铺设总管→冲孔→用弯联管将井点管与总管接通→安装井点管、填砂砾滤料、上部填黏土密封→安装抽水设备与总管连通→安装集水箱和排水管→测量观测井中地下水位变化
B．放线定位→铺设总管→冲孔→安装井点管、填砂砾滤料、上部填黏土密封→用弯联管将井点管与总管接通→安装抽水设备与总管连通→安装集水箱和排水管→开动真空泵排气、再开动离心水泵抽水→测量观测井中地下水位变化
C．放线定位→铺设总管→冲孔→安装井点管、填砂砾滤料、上部填黏土密封→用弯联管将井点管与总管接通→安装集水箱和排水管→开动真空泵排气、再开动离心水泵抽水→测量观测井中地下水位变化
D．放线定位→铺设总管→冲孔→用弯联管将井点管与总管接通→安装抽水设备与总管连通→安装集水箱和排水管→开动真空泵排气、再开动离心水泵抽水→测量观测井中地下水位变化
查看答案
单项选择题

Scientific research that involves international collaboration has produced papers of greater influence, as measured by the number of times a paper is cited in subsequent papers, than has research without any collaboration. Papers that result from international collaboration are cited an average of seven times, whereas papers with single authors are cited only three times on average. This difference shows that research projects conducted by international research teams are of greater importance than those conducted by single researchers.
Which one of the following is an assumption on which the argument depends

A．Prolific writers can inflate the number of citations they receive by citing themselves in subsequent papers.

B．It is possible to ascertain whether or not a paper is the product of international collaboration by determining the number of citations it has received.

C．The number of citations a paper receives is a measure of the importance of the research it reports.

D．The collaborative efforts of scientists who are citizens of the same country do not produce papers that are as important as papers that are produced by international collaboration.

E．(E) International research teams tend to be more generously funded than are single researchers.
查看答案