问题 填空题
给出定义:若m-
1
2
<x≤m+
1
2
(其中m为整数),则m叫做离实数x最近的整数,记作{x}=m.下列关于函数f(x)=|x-{x}|的四个命题:
①函数y=f(x)的定义域为R,值域为[0,
1
2
];
②函数y=f(x)在[-
1
2
1
2
]上是增函数;
③函数y=f(x)是周期函数,最小正周期为1;
④函数y=f(x)的图象关于直线x=
k
2
(k∈Z)对称.
其中正确命题的序号是______.
答案

①∵m-

1
2
<x≤m+
1
2
(其中m为整数),

-

1
2
<x-m≤
1
2
,∴0≤|x-m|≤
1
2

∴函数f(x)=|x-{x}|=|x-m|的值域为[0,

1
2
].

②由定义知:当x=-

1
2
时,m=-1,∴f(-
1
2
)=|-
1
2
-(-1)|=
1
2

-

1
2
<x≤
1
2
时,m=0,∴f(x)=|x-0|=|x|
1
2

故f(x)在[-

1
2
1
2
]上不是增函数,所以②不正确.

③由-

1
2
<x-m≤
1
2
-
1
2
<(x+1)-(m+1)≤
1
2

∴{x+1}={x}+1=m+1,∴f(x+1)=|(x+1)-{x+1}|=|x-{x}|=f(x),

所以函数y=f(x)是周期函数,最小正周期为1.

④由②可知:在x∈[-

1
2
1
2
]时,f(x)=|x|关于y周对称;

又由③可知:函数y=f(x)是周期函数,最小正周期为1,

∴函数f(x)的图象关于直线x=

k
2
(k∈Z)对称.

故答案为①③④.

改错题

短文改错。

假定英语课上老师要求同桌之间交换修改作文,请你修改你同桌写的以下作文。文中共

有10处语言错误,每句中最多有两处。每处错误涉及一个单词的增加、删除或修改。

增加:在缺词处加一个漏字符号(∧),并在其下面写出该加的词。

删除:把多余的词用斜线(/)划掉。

修改:在错的词下划一横线,并在该词下面写出修改后的词。

注意:

1.每处错误及其修改均仅限一词;

2. 只允许修改10处,多者(从第11处起)不计分。

Dear friends,

     I'm awfully sorry to hear that horrible and severe earthquake unexpectedly hit your hometown.

Faced with such a rarelyseen disaster, you remain as calm and strongwilled that we are all moved

to tear. A friend in need is a friend indeed. Think about your present situation, you can not wait a

minute to make every bit of our effort to help you. I, as for chairman of the Students' Union, on

behalf of all my schoolmates, express our most sincerely pity and care for you. Besides, we made

a donation of 120,000 yuan to you, expecting that it can help you go through the difficult. A better

hometown can be rebuilt. Remember we won't  be far away as you need any help!

                                                                                      Yours sincerely,

                                                                                              Li Hua

_______________________________________________________________________________

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