问题 选择题
如果不等式组
x≥0
y≥2x
kx-y+1≥0
表示的平面区域是一个直角三角形,则该三角形的面积为(  )
A.
1
2
1
5
B.
1
2
1
3
C.
1
5
1
4
D.
1
4
1
2
答案

解:有两种情形:

(1)直角由y=2x与kx-y+1=0形成(如图),则

∵2×k=-1,∴k= ,y=2x与x-y+1=0的交点坐标为( ),

三角形的三个顶点为(0,0),(0,1),( ),

∴该三角形的面积为S=

(2)直角由x=0与kx-y+1=0形成(如图),

则k=0,

∴由x=0与-y+1=0交于点( ,1)三角形的三个顶点为(0,0),(0,1),( ,1),

∴该三角形的面积为S= ×1×=

综上所述,三角形的面积为

  故选C

阅读理解

阅读理解。

     108 cities in China took part in the World Car Free Day on Saturday to promote environmentally

friendly transport and ease increasingly grid-locked city streets.  It's a highlight of a nationwide urban

public transport week. People were urged to take public transport,ride bikes or walk.

      To help out,more than 200 new buses took to the streets. And the Beijing Subway laid on 10 more

trains for rush hour.

      A Beijing resident said,"Today is car free day,and I do find the traffic much better and the bus can

go much faster. "

      Another resident said,"I spent only half an hour going to work. It took me twice as long before,and

I can find seat on the bus today. "

      But in some areas not signed up for traffic control,endless lines of cars can still be seen.

     Some people say they just can't do without their cars.

     Another Beijing resident said,"Some people are willing to give up driving,but on certain days when I

have to take my child to school or weekend classes,the public transport is so bad that I can't do it without a car. "

       But the concept of "green"traffic is catching on. People say they believe it's the first and honest step

in facing the serious traffic and environmental problems.

      A driver said,"The car free day has a very important symbolic meaning. It does not mean that we must give up cars. It is to promote a concept,to encourage more people to contribute to the protection of the

environment. "

     The Ministry of Construction calculates"Car Free Day"will cut 3,000 tons of emissions and save 33

million liters of gasoline.  And it's planning more frequent activities to raise public consciousness of energy

conservation and environmental protection.   

1. The best title of the passage is possibly _______ 

A. Private cars are banned in cities    

B. Car-free Day pushes"green"transport

C. Residents can't do without cars    

D. Residents should ride bikes on Car-free Day 

2. Car-free Day will bring the following benefits except _______.

A. saving quite a lot of energy          

B. raising public consciousness of environmental protection

C. improving road traffic                

D. facing more serious traffic problems

3. What do you think is possibly the author's attitude towards the Car-free Day?

A. Positive.      

B. Negative.        

C. Passive.          

D. Critical.

单项选择题