灯下 登录
数学 / 几何原本 / Proposition X.8

第10卷命题 8 · 无理量判定定理

If two magnitudes have not to one another the ratio which a number has to a number, the magnitudes will be incommensurable.

若两量之比不等于两数之比,则两量不可公度。

A B
fig-1

本页以“无理量判定定理”整体图解辅助阅读;点、线、角、圆索引已按命题文字和证明步骤校订,可与证明和问答联动。

线

正文图形由校订坐标生成;点、线、角、圆可与证明和问答联动。

分步证明Step-by-step proof
1 / 4
  1. For let the two magnitudes A, B not have to one another the ratio which a number has to a number; I say that the magnitudes A, B are incommensurable.

    设两量A、B之比不等于两数之比。

  2. For, if they are commensurable, A will have to B the ratio which a number has to a number.

    假设A、B可公度,则根据X.5,A与B之比等于两数之比。

  3. [X. 5] But it has not; therefore the magnitudes A, B are incommensurable.

    但假设中A与B之比不等于两数之比,矛盾。

  4. 因此A、B不可公度。