对于函数f（x）=sinπx,x∈0.212fx-2,x∈2,+∞，有下列4个命题：①任取x1、x2∈[0，+∞），都有|f（x1）﹣f（x2）|≤2恒成立；②f（x）=2kf（x+2k）（k∈N*）

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对于函数f（x）=sinπx,x∈0.2

1

2

fx-2,x∈2,+∞，有下列4个命题：

①任取x₁、x₂∈[0，+∞），都有|f（x₁）﹣f（x₂）|≤2恒成立；

②f（x）=2kf（x+2k）（k∈N^*），对于一切x∈[0，+∞）恒成立；

③函数y=f（x）﹣ln（x﹣1）有3个零点；

④对任意x＞0，不等式f（x）≤

k

x

恒成立，则实数k的取值范围是[

9

8

，+∞）．

则其中所有真命题的序号是____

上一题下一题 0.0难度选择题更新时间:2017-10-25 09:31:42

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①③

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There are many different ways to travel to Paris from London. One of the quickest and most popular ways is by train. From Waterloo Railway station, you can travel all the way to Paris. The journey takes about three hours. The train, called the Eurostar, is very modern, and the seats are comfortable.
You can also travel to France by ship. First, you go to Dover, on the coast (海岸), by bus from London. The bus stops at the Ferry Terminal Seven in Dover. You can buy your tickets there. People who travel by car can drive on to the ferry (渡轮), too.
Another way to travel to Paris is by plane. There are several airports with international flights to Paris and other cities in France. You can travel to London Airport by bus or underground. Some people even go by taxi but this is a very expensive way to travel!

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