Greek letters, like Latin letters and Cyrillic letters, are phonemic characters. Cyrillic alphabet and Georgian alphabet used in Russian, Ukrainian, etc. They are all developed from Greek letters, which are derived from Phoenician letters, while Phoenician letters have only consonants and are written from right to left. Greek developed vowels, so the Greeks added vowels.
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Greek letters are often used in mathematics, science, engineering and other fields. In mathematics, Greek letters are usually used to represent constants, special functions and some specific variables. In the field of mathematics, the meanings of uppercase and lowercase Greek letters are usually different and irrelevant.