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数学 / 几何原本 / Proposition X.7

第10卷命题 7 · 不可通约量无数量比

Incommensurable magnitudes have not to one another the ratio which a number has to a number.

不可通约的量之间不具有一个数与另一个数之比。

A B
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分步证明Step-by-step proof
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  1. Let A, B be incommensurable magnitudes; I say that A has not to B the ratio which a number has to a number.

    设A、B为不可通约的量。

  2. For, if A has to B the ratio which a number has to a number, A will be commensurable with B.

    假设A与B之比等于一个数与另一个数之比。

  3. [X. 6] But it is not; therefore A has not to B the ratio which a number has to a number.

    根据X.6,则A与B可通约。

  4. 但A与B不可通约,矛盾,故假设不成立。