给出以下四个命题：
（1）对于任意的a＞0，b＞0，则有algb=blga成立；
（2）直线y=x•tanα+b的倾斜角等于α；
（3）在空间如果两条直线与同一条直线垂直，那么这两条直线平行；
（4）在平面将单位向量的起点移到同一个点，终点的轨迹是一个半径为1的圆．
其中真命题的序号是______．
（1）中，∵a＞0，b＞0，若algb=blga，则lgalgb=lgblga，即lgb•lga=lga•lgb成立，∴命题正确；
（2）中，直线y=x•tanα+b的斜率是k=tanα，当α∈[0，π）且α≠
时，倾斜角等于α，否则，命题不成立；π 2
（3）中，在空间如果两条直线与同一条直线垂直，那么这两条直线不一定平行，也可能异面或相交，∴命题不成立；
（4）中，∵单位向量的模长是1，∴在平面内将单位向量的起点移到同一个点，终点的轨迹是一个半径为1的圆，命题正确；
∴正确的命题有（1）（4）；
故答案为：（1）（4）．
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| The books in David's schoolbag felt like bricks as he ran down the street. What he wanted to do was to play basketball with Eric, 1 his mother told him he would have to return his sister's books to the library first. He had 2 set foot in a library and he wasn't about to do so today. He would just 3 the books in the outside return box. But there was a 4 : it was locked. He went into the building, only a few minutes 5 closing time. He put the books into the return box. And after a brief 6 in the toilet, he would be on his way to the playground to 7 Eric. David stepped out of the toilet and stopped in 8 - the library lights were off. The place was 9 . The doors had been shut. They 10 be opened from the inside, he was trapped(被困) - in a library! He tried to 11 a telephone call, but was unable to 12 . What's more, the pay phones were on the outside of the building. 13 the sun began to set, he searched for a light and found it. 14 he could see. David wrote on a piece of paper: " 15 ! I'm TRAPPED inside!" and stuck it to the glass door. 16 , someone passing by would see it. He was surprised to discover that this place was not so unpleasant 17 . Rows and rows of shelves held books, videos and music. He saw a book about Michael Jordan and took it off the shelf. He settled into a chair and started to 18 . He knew he had to 19 , but now, that didn't seem to be such a 20 thing. | ||||
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