實數里的“實”是什么意思，誰能想到是“真實”的意思？實數 Real number，就是真實存在的數字，實數是在虛數這個概念出現之后才有的，實數是相對虛數來說的。

1 英語愿意

實數：Real number

2 英文解釋

2.1 What is a Real number?

A real number is any number that can be placed on a number line or expressed as in infinite decimal expansion. In other words, a real number is any rational or irrational number, including positive and negative whole numbers, integers, decimals, fractions, and numbers such as pi (π) and Euler’s number (e).

實數是可以放在數字線上或以無限十進制展開表示的任何數字。換句話說，實數是任何有理數或無理數，包括正負整數、整數、小數、分數和數字，例如 pi （π） 和歐拉數 （e）。

In contrast, an imaginary number or complex number is not a real number. These numbers contain the number i, where i2 = -1.

相反，虛數或復數不是實數。這些數字包含數字 i，其中 i2 = -1。

Real numbers are represented by the capital letter “R” or double struck typeface . The real numbers are an infinite set of numbers.

2.2 Why are they called "Real" Numbers?

Because they are not Imaginary Numbers.

因為它們不是虛數。

The Real Numbers had no name before Imaginary Numbers were thought of. They got called "Real" because they were not Imaginary. That is the actual answer!

在虛數出現之前，實數是沒有名字的。它們被稱為“真實”，因為它們不是虛構的。這才是真正的答案！

3 中文解釋

實數，是有理數和無理數的總稱。

要想深刻理解這些專業術語，一定要看英語原意啊，明明通俗易懂的英語詞語，翻譯成中文之后就變得晦澀難懂。