1
the letter sigma
在数学和统计中，西格玛常用来表示求和符号 ∑。
The letter sigma is the 18th letter of the Greek alphabet.
字母西格玛是希腊字母表中的第十八个字母。
西格玛；σ
先理解核心含义，再看它在真实句子里的用法。
西格玛；σ
the 18th letter of the Greek alphabet
The letter sigma is the 18th letter of the Greek alphabet.
字母西格玛是希腊字母表中的第十八个字母。
The eighteenth letter of the Classical and Modern Greek alphabets (Σ, σ), the twentieth letter of Old and Ancient.
The symbol Σ, used to indicate summation of a set or series.
The symbol σ, used to indicate one standard deviation from the mean, particularly in a normal distribution.
The eighteenth letter of the Greek alphabet is sigma, which comes after rho.
希腊字母表的第十八个字母是西格玛，排在rho之后。
Our teacher wrote a small sigma on the board and asked us to pronounce it.
老师在黑板上写了一个小写的西格玛，让我们读出来。
There are two forms of the lowercase sigma in Greek handwriting.
在希腊语手写体中，小写西格玛有两种形式。
在数学和统计中，西格玛常用来表示求和符号 ∑。
The letter sigma is the 18th letter of the Greek alphabet.
字母西格玛是希腊字母表中的第十八个字母。
两种复数形式 sigmas 和 sigmata 都正确。
The plural of sigma is sigmas or sigmata.
西格玛的复数是 sigmas 或 sigmata。
Not this
There are 24 sigma in the Greek alphabet.
Use this
There are 24 sigmas in the Greek alphabet.
英语可数名词在表示“多个”时要加复数词尾 -s；sigma 是可数名词，汉语没有复数变化，容易漏掉复数，所以应写 sigmas。
Not this
I need to calculate the sigma of these numbers.
Use this
I need to calculate the sum of these numbers.
sigma 指希腊字母“西格玛”（或求和符号），不是加法计算的结果；表示“总和、和”时应使用 sum。