题干

已知直线l过点P(3,4)且与直线2x﹣y﹣5=0垂直,则直线l的方程为____.
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答案(点此获取答案解析)

x+2y﹣11=0

同类题3

阅读下面短文,掌握其大意,然后从每题所给的A、B、C、D四个选项中选出最佳选项。

    My six-year-old daughter, Cindy, and I stopped at a food shop for some bread. As we were going out of the door, a young teenage boy was coming in.

    The boy had a strange hairstyle. His nose was pierced, and a ring ran 1 the hole. He held a skateboard under one arm and a2 under the other.

    Cindy, who was walking ahead of me, suddenly 3 when she saw the boy. I thought he had frightened my daughter. But I was 4. My daughter backed up against the door and opened it as wide as it would go. Now I came face to face with the young man. I 5 aside (到一边) and let him pass. He replied vey 6, “Thank you very much.”

    On our way to the car, I praised Cindy for holding open the door for the boy. It seemed that she was not troubled by the boy's appearance,7 I still wanted to make sure. I wanted to be ready to talk about the young man 8 was so different from others.     I prepared to tell my little daughter what 9should be like.   

    But as it turned out, the person who needed the talk was 10!

    The only thing Cindy noticed about the boy was the fact that his arms were 11. “ He held a skateboard under one arm and a basketball under the other. He would have a 12 time to open the door,” said Cindy.

    I just 13  the hairstyle, the piercing and the ring, while she saw a person carrying something under arms and heading towards a(an)14 door.

    What my daughter said 15 me that I should change my ways of judging people and learn from my daughter to be open-minded and warm-hearted.

同类题4

关于遗传物质的探索:

(一) R型肺炎双球菌菌体无多糖类的荚膜,是无毒性细菌;S型肺炎双球菌菌体有多糖类的荚膜,是有毒性细菌,使人患肺炎或使小鼠患败血症.科学家艾弗里及其同事利用肺炎双球菌来探究什么是遗传物质的问题.实验材料、用具:S型细菌、DNA水解酶、培养基、培养器等.

艾弗里等人先做了三组实验:

①S型细菌的蛋白质+R型活细菌R型菌落;

②S型细菌荚膜的多糖+R型活细菌R型菌落;

③S型细菌的DNA+R型活细菌R+S型菌落;

(1)艾里弗等人后来发现上述实验步骤并不严密,于是又做了第四组实验,请按照①②③中表达式写出第四组实验方法和结果:④____ 

(2)从上述实验可以得出结论____ 

(3)肺炎双球菌具有的细胞器是____ 

(4)肺炎双球菌与酵母菌在结构上的主要区别是:____ 

(二)做噬菌体侵染细菌实验时,用放射性同位素标记某个噬菌体和细菌的有关物质如下表.产生的100个子代噬菌体与亲代噬菌体的形状、大小完全一样.试回答:


噬菌体

细菌

核苷酸

32P标记

31P

氨基酸

32S

35S标记

(1)子代噬菌体中,只含有32P的有____ 个,只含有31P的有____ 个,同时含有32P和31P的有____ 个.

(2)子代噬菌体的蛋白质分子中,都没有____ 元素,由此说明____;子代噬菌体的蛋白质分子都含有____ 元素,这是因为____ 

(3)实验中用放射性同位素标记噬菌体时,选取35S和32P这两种同位素分别标记蛋白质和DNA,能否用14C和18O标记?____(能或不能)说明理由:____