搜题请搜索小程序“爱下问搜题”
问题 解答题

已知一元二次方程2x2+4x-3=0．

（1）不解方程，试说明该方程有两个不相等的实数根；

（2）设x1，x2是此方程的两个根，求（x1+1）（x2+1）的值．

答案

解（1）∵△=42-4×2×（-3）=16+24=40＞0…（3分）

∴原方程有两个不相等的实数根．…（4分）

（2）∵x1+x2=-2，x1•x2=-

3
2
…（6分）

∴（x1+1）（x2+1）=x1+x2+x1x2+1

=-

5
2
…（8分）

完形填空

Many people say that they have seen flying saucers（飞碟）in the sky.   31  can these things be ?

Some people think that they are spaceships from other planets. Doctors   32  that perhaps they are only a weakness of the eyes. It is possible that they are our own planes   33  very high. Or are they birds with the sun’s light on them?

But some people say that they have seen them   34 . They have seen beings（人）get off them and walk around. They have   35   to those beings, sometimes in English. People have   36   photos of flying saucers and of these beings. We have seen the photos, but sometimes the people had to take them in a   37 . Children have seen flying saucers, and even dogs have seen them. Perhaps we do not think that the   38  of children, or dogs are important. But school-teachers have   39  seen them and Air Force officers and   40  policemen. Must we not listen to these people?

小题1:  

A．How

B．What

C．Which

D．Where小题2:  

A．say

B．prove

C．know

D．understand小题3:  

A．rising

B．flying

C．risen

D．flown小题4:  

A．fly

B．turn

C．land

D．move小题5:  

A．flown

B．gone

C．come

D．spoken小题6:  

A．received

B．bought

C．taken

D．sent小题7:  

A．horse

B．hurry

C．colour

D．way小题8:  

A．opinions

B．discussions

C．suggestions

D．needs小题9:  

A．often

B．hardly

C．also

D．still小题10: 

A．yet

B．even

C．so

D．then
查看答案
选择题

如图所示，在磁感应强度为B的匀强磁场中，有一个边长为L的正方形线框，线框平面与磁场垂直，下列说法正确的是

A．此时穿过线框的磁通量为BL2

B．若线框向右平移，由于左、右边切割磁感线，线框中有感应电流产生

C．若将线框翻转180°，该过程磁通量的变化为0，该过程无感应电流产生

D．将线框绕其中一边向外转90°，磁通量的变化为BL2，该过程中有感应电流产生
查看答案