5 sentences

1. 阿尔法是第一个希腊字母。

   ā'ěr​fǎ shì dì​yī​gè Xī​là zì​mǔ.

   Alpha is the first letter of the Greek alphabet.

   Source: Dong Chinese Dictionary

2. 纽是希腊字母表中的一个字母。

   niǔ shì Xī​là zì​mǔ​biǎo zhōng de yī gè zì​mǔ.

   Nu is a letter in the Greek alphabet.

   Source: Dong Chinese Dictionary

3. 斐是希腊字母表中的第21个字母。

   fěi shì Xī​là zì​mǔ​biǎo zhōng de dì21 gè zì​mǔ.

   Phi is the 21st letter of the Greek alphabet.

   Source: Dong Chinese Dictionary

4. 他在笔记本上写下了一个希腊字母凯。

   tā zài bǐ​jì​běn shàng xiě​xià le yī gè Xī​là zì​mǔ kǎi.

   He wrote down the Greek letter Chi in his notebook.

   Source: Dong Chinese Dictionary

5. 在数学公式中，我们常用希腊字母套来表示常数。

   zài shù​xué gōng​shì zhōng, wǒ​men cháng​yòng Xī​là zì​mǔ tào lái biǎo​shì cháng​shù.

   In mathematical formulas, we often use the Greek letter tau to represent constants.

   Source: Dong Chinese Dictionary