下面是关于函数f（x）=|x﹣{x}|的四个命题：①函数y=f（x）的定义域是R，值域是 $0,\frac{1}{2}$ ；②函数y=f（x）的图象关于直线 $x=\frac{k}{2}\left(k\in Z\right)$ 对称；③函数y=f（x）是周期函数，最小正周期是1；其中正确的命题序号是____．

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Never try to work when you are very hungry. If you decided to do your homework right after school, you may get something to eat before getting to work. Always do your homework before you get too tired. Don't wait until very late in everything, or your work will seem much harder than it really is.

    If you have more than an hour's work, give yourself a break after an hour. On the other hand, don't break it up so much, or you can't finish anything, you should be able to work at least a half at a time without stopping.

    Don't put it off until the last minute. If you put off doing your homework, you will have it on your mind, and you will not enjoy your free time so much. If you put it off until the end of the week or until right before a test, you will have too much work to do. A little bit each night, enough to keep up with what is happening each day in school, will make you not afraid of the test and get good grades.

Do your homework at the same time every evening. This will help you make it a habit. It will make it easier to do, and it will make your free time more enjoyable, as well.