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数学 / 几何原本 / Proposition VII.29

第7卷命题 29 · 素数不测则互素

Any prime number is prime to any number which it does not measure.

如果一个素数不度量另一个数,那么这两个数互素。

A B C
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分步证明Step-by-step proof
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  1. Let A be a prime number, and let it not measure B; I say that B, A are prime to one another. For, if B, A are not prime to one another, some number will measure them.

    设A是素数,且A不度量B。假设B和A不互素,则存在某个数C度量它们。

  2. Let C measure them.

    由于C度量B,而A不度量B,因此C与A不同。

  3. Since C measures B, and A does not measure B, therefore C is not the same with A. Now, since C measures B, A, therefore it also measures A which is prime, though it is not the same with it: which is impossible.

    因为C度量B和A,所以C也度量素数A,但C与A不同,这是不可能的。

  4. Therefore no number will measure B, A.

    因此,没有数能度量B和A,即B和A互素。