题干

如图,铁路上A、B两点相距25km,C、D为两村庄,DA⊥AB于A,CB⊥AB于B,已知DA=15km,CB=10km,现在要在铁路AB上建一个土特产品收购站E,使得C、D两村到E站的距离相等,则E站应建在距A站多少千米处?

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答案(点此获取答案解析)

解:设AE=xkm,

∵C、D两村到E站的距离相等,∴DE=CE,即DE2=CE2

由勾股定理,得152+x2=102+(25﹣x)2,x=10.

故:E点应建在距A站10千米处.

同类题3

根据短文理解,选择正确答案。

    At thirteen, I was diagnosed(诊断) with kind of attention disorder. It made school difficult for me. When everyone else in the class was focusing on tasks, I could not.

    In my first literature class, Mrs. Smith asked us to read a story and then write on it, all within 45 minutes. I raised my hand right away and said, “Mrs. Smith, you see, the doctor said I have attention problems. I might not be able to do it.”

    She glanced down at me through her glasses, “You are not different from your classmates, young man.”

    I tried, but I didn't finish the reading when the bell rang. I had to take it home. In the quietness of my bedroom, the story suddenly all became clear to me. It was about a blind person, Louis Braille. He lived in a time when the blind couldn't get much education. But Louis didn't give up. Instead, he invented a reading system of raised dots(点), which opened up a whole new world of knowledge to the blind.

    Wasn't I the “blind” in my class, being made to learn like the “sighted” students? My thoughts spilled out and my pen started to dance. I completed the task within 40 minutes. Indeed, I was no different from others; I just needed a quieter place. If Louis could find his way out of his problems, why should I ever give up?

    I didn't expect anything when I handled in my paper to Mrs. Smith, so it was quite a surprise when it came back to me the next day- with an “A” on it. At the bottom of the paper were these words: “See what you can do when you keep trying?”