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mc1-020 · ENGLISH LEARNING

3-4-5 三角形问题The 3-4-5 Triangle Problem

英语学习拓展 约 12 分钟阅读 中文English

内容概述

  • 数学故事
  • 几何证明 / 数学问题
  • 叙事 + 图注 + 证明思路

本文提出一个经典几何问题:在不使用勾股定理及其逆定理或任何推论的前提下,证明 3-4-5 三角形是直角三角形。文章指出古埃及测量员可能用打有 11 个结的绳子(分为 12 等份)来构造 3-4-5 直角三角形,但并无文字证据表明他们知晓勾股定理。随后介绍了一种基于面积法的简洁证明:将四个 3-4-5 直角三角形与一个单位正方形拼成一个大正方形(面积为 25),从而推出斜边长为 5。该解法见于中国古代数学经典《周髀算经》,且可推广至任意直角三角形的勾股关系。

中文正文

20° 3-4-5 三角形问题

有报告说,古埃及的测量员会拿一根绳子来打 11 个结,把它等分为 12 节,通过这样来构造 3-4-5 直角三角形。因为没有文字证据说明古埃及人懂得毕达哥拉斯定理(哪怕它的一个特例),于是我们自然提出下面的问题:不用毕达哥拉斯定理和它的任何相关结论,如何证明 3-4-5 三角形是直角三角形?读者也许有兴趣来试试。千百年来,我们有了很多证明方法。图 3 大致说明了一个特别简单的方法。四个边长分别为 3 和 4 的直角三角形紧贴在一个单位正方形的四边,形成一个面积等于 25(平方单位)的正方形。这意味着直角三角形斜边的长为 5,从而 3-4-5 三角形是直角三角形。这个解法见《周髀算经》(The Arithmetical Classic of the Gnomon and the Circular Paths of Heaven),一般认为是最古老的中国古代数学经典,很容易推广去得到任意直角三角形的毕达哥拉斯关系。

图 3
图 3

图 3 四个 3-4-5 直角三角形与中心单位正方形拼成大正方形(面积 = 25)

英文正文

20° The 3-4-5 triangle problem. There are reports that ancient Egyptian surveyors laid out right angles by constructing 3–4–5 triangles with a rope divided into 12 equal parts by 11 knots. Since there is no documentary evidence to the effect that the Egyptians were aware of even a particular case of the Pythagorean theorem, the following purely academic problem arises: Show, without using the Pythagorean theorem, its converse, or any of its consequences, that the 3–4–5 triangle is a right triangle. The reader may care to try to solve this problem. Many different solutions have been given over the years. A particularly simple solution can be effected based on Figure 3, which shows four right triangles with legs of 3 and 4 units, along with a unit square, making up a square of 25 square units of area. This means that the hypotenuse of a right triangle with legs of 3 and 4 units is 5 units long, and it follows that a 3–4–5 triangle is a right triangle. This solution is found in the Chou-pei Suan-king (The Arithmetical Classic of the Gnomon and the Circular Paths of Heaven), a work generally regarded as the oldest of the ancient Chinese mathematical classics. The solution is easily generalized to obtain the Pythagorean relation for an arbitrary right triangle.

英语学习拓展

常用词汇

重点 · 近义词拓展
surveyor

音标/səˈveɪər/

释义与用法

测量员。

原文用法:"ancient Egyptian surveyors laid out right angles..."

查看对应近义词组 ↓

lay out:布置,铺设,划定。原文用法:"ancient Egyptian surveyors laid out right angles by constructing..."

重点 · 近义词拓展
documentary

音标/ˌdɑːkjuˈmentri/

释义与用法

文献的,文件的。

原文用法:"Since there is no documentary evidence to the effect that..."

查看对应近义词组 ↓
重点 · 近义词拓展
converse

音标/kɒnvɜːrs/

释义与用法

(逻辑学)逆命题。

原文用法:"...without using the Pythagorean theorem, its converse, or any of its consequences..."

查看对应近义词组 ↓
consequence

音标/ˈkɒnsɪkwens/

释义与用法

推论,结果。

原文用法:"...its converse, or any of its consequences..."

effect

音标/ɪˈfɛkt/

释义与用法

效果;大意(在此短语中)。

原文用法:"no documentary evidence to the effect that..."(意为"没有……内容的文献证据")

重点 · 近义词拓展
arise

音标/əˈraɪz/

释义与用法

出现,产生。

原文用法:"the following purely academic problem arises"

查看对应近义词组 ↓
purely

音标/ˈpjʊrli/

释义与用法

纯粹地。

原文用法:"the following purely academic problem arises"

effect

音标/ɪˈfɛkt/

释义与用法

实现,达成。

原文用法:"A particularly simple solution can be effected based on Figure 3..."

leg

音标/lɛg/

释义与用法

(直角三角形的)直角边。

原文用法:"four right triangles with legs of 3 and 4 units..."

hypotenuse

音标/haɪˈpɒtənuːz/

释义与用法

(直角三角形的)斜边。

原文用法:"This means that the hypotenuse of a right triangle with legs of 3 and 4 units is 5 units long..."

重点 · 近义词拓展
generalize

音标/ˈdʒɛnrəlaɪz/

释义与用法

推广,概括。

原文用法:"The solution is easily generalized to obtain the Pythagorean relation..."

查看对应近义词组 ↓
arbitrary

音标/ˈɑːrbɪtreri/

释义与用法

任意的。

原文用法:"...for an arbitrary right triangle."

gnomon

音标/ˈnoʊmɒn/

释义与用法

圭表(日晷的指针部件)。

原文出处书名:"The Arithmetical Classic of the Gnomon and the Circular Paths of Heaven"

同义词与近义词

surveyor/measurer/land-surveyor

对应核心词汇:surveyor

用法辨析

对应核心词汇:surveyor

辨析:surveyor 最通用;measurer 更侧重"测量行为"本身;land-surveyor 特指土地测量员。

documentary/written/textual

对应核心词汇:documentary

用法辨析

对应核心词汇:documentary

辨析:documentary 强调"有文件/文献记录";written 强调"书面形式";textual 强调"文本性质"。

converse/inverse/reverse

对应核心词汇:converse

用法辨析

对应核心词汇:converse

辨析:在逻辑中,converse 指"逆命题"(交换条件和结论);inverse 指"否命题"(分别否定条件和结论);reverse 指"相反/颠倒"(通用词)。

arise/emerge/occur

对应核心词汇:arise

用法辨析

对应核心词汇:arise

辨析:arise 较正式,常用于"问题/困难出现";emerge 侧重"从隐藏状态显现";occur 最通用。

generalize/extend/extrapolate

对应核心词汇:generalize

用法辨析

对应核心词汇:generalize

辨析:generalize 指从特殊到一般;extend 指扩大适用范围;extrapolate 指从已知数据外推到未知范围。

常用短语与固定搭配

  • lay out:布置,规划,铺设。原文用法:"ancient Egyptian surveyors laid out right angles by constructing 3–4–5 triangles..."
  • to the effect that:大意是,内容为。原文用法:"no documentary evidence to the effect that the Egyptians were aware of..."
  • be aware of:知道,意识到。原文用法:"the Egyptians were aware of even a particular case of the Pythagorean theorem"
  • care to do something:愿意做某事(常用于礼貌邀请)。原文用法:"The reader may care to try to solve this problem."
  • based on:基于,以……为基础。原文用法:"A particularly simple solution can be effected based on Figure 3..."
  • make up:组成,构成。原文用法:"...along with a unit square, making up a square of 25 square units of area."
  • it follows that:由此可见,从而得出。原文用法:"...and it follows that a 3–4–5 triangle is a right triangle."

常用句式

  • There are reports that...:有报告称……(表达未经完全证实的信息)。原文例句:"There are reports that ancient Egyptian surveyors laid out right angles..."
  • Since there is no evidence to the effect that..., ...:既然没有……内容的证据,那么……(证据缺失 → 谨慎结论)。原文例句:"Since there is no documentary evidence to the effect that the Egyptians were aware of..., the following purely academic problem arises"
  • Show, without using ..., that...:证明/说明……,但不使用……(数学问题中的限制条件表述)。原文例句:"Show, without using the Pythagorean theorem, its converse, or any of its consequences, that the 3–4–5 triangle is a right triangle."
  • This means that..., and it follows that...:这意味着……,从而得出……(推理链中的连续推导)。原文例句:"This means that the hypotenuse...is 5 units long, and it follows that a 3–4–5 triangle is a right triangle."

长难句解析

"Since there is no documentary evidence to the effect that the Egyptians were aware of even a particular case of the Pythagorean theorem, the following purely academic problem arises: Show, without using the Pythagorean theorem, its converse, or any of its consequences, that the 3-4-5 triangle is a right triangle."

  • 主干:problem arises(问题出现了)
  • 修饰与从句:

- "Since there is no documentary evidence to the effect that..." —— 原因状语从句 - "to the effect that the Egyptians were aware of..." —— 修饰 evidence 的不定式短语,内含同位语从句说明 evidence 的内容 - "the following purely academic problem arises:" —— 主句 - "Show, without using..., that..." —— 冒号后的问题陈述(Show 的宾语从句 "that the 3-4-5 triangle is a right triangle") - "without using the Pythagorean theorem, its converse, or any of its consequences" —— 插入的限制性状语

  • 逻辑关系:原因(Since 无证据)→ 结果(问题 arises:需在不使用 XXX 的前提下证明 YYY),典型的"限制条件下的证明问题"表述。

"A particularly simple solution can be effected based on Figure 3, which shows four right triangles with legs of 3 and 4 units, along with a unit square, making up a square of 25 square units of area."

  • 主干:A particularly simple solution can be effected(一个特别简单的解法可以被实现/给出)
  • 修饰与从句:

- "based on Figure 3," —— 方式状语 - "which shows four right triangles with legs of 3 and 4 units, along with a unit square," —— 非限制性定语从句,修饰 Figure 3 - "making up a square of 25 square units of area." —— 现在分词短语作结果状语,说明图中各元素共同组成的大图形

  • 逻辑关系:方法(based on Figure 3)→ 图的内容(which shows...)→ 结果(making up a square of 25...)→ 结论(solution can be effected)

语言使用特点

  • 本文属于数学问题陈述(mathematical problem statement) 文体,特点是:条件限定精确("without using...")、术语使用规范(converse, consequence, hypotenuse, legs, generalize, arbitrary)、逻辑衔接紧密(Since → arises → Show → This means → it follows)。
  • 使用了典型的数学指令动词:Show(证明/说明)、effected(实现/完成)。这些动词在数学英语中有固定的搭配模式。
  • 书名使用斜体并附英文译名(Chou-pei Suan-king (The Arithmetical Classic of the Gnomon and the Circular Paths of Heaven)),符合学术引用规范。
  • "may care to try" 是一种委婉的表达方式,相当于"读者不妨试试",体现了作者对读者的尊重和鼓励态度。

迁移练习

  1. there is no evidence to the effect that 写一句话,描述一个历史上尚未证实的事件。
  2. 将以下中文翻译成英文,尽量使用本文句式:"由于没有文献记载表明古希腊人知道无理数的一般定义,以下问题自然出现了:证明 √2 不能表示为两个整数的比值。"
  3. 用英文描述图 3 的构造过程,至少使用 legshypotenuseunit squaremake up 这四个词语。
点击展开参考答案
  1. (示例)There is no evidence to the effect that the ancient Egyptians used zero as a placeholder in their numeral system.
  2. (示例)Since there is no documentary evidence to the effect that the ancient Greeks knew the general definition of irrational numbers, the following problem naturally arises: Show that √2 cannot be expressed as a ratio of two integers.
  3. (示例)Figure 3 shows four right triangles with legs of 3 and 4 units arranged around a central unit square, together making up a larger square. The hypotenuse of each triangle forms one side of the outer square.