I speak reasonably fluent Greek (family language), and took a course in Classical Greek when I was in school. My professor explained that the pronunciations used in mathematics (tau, beta, mu...) differ from the Modern Greek versions (taf, veeta, mee...) because the former are the (conjectured) pronunciations used in the classical language. A large source of evidence for the pronunciation of Classical Greek is the transliteration of Greek words in to other languages during that period, especially into Latin. The whole language is pronounced very differently, not just the alphabet.
As a side note, that class was absurdly easy because I already knew almost all the vocabulary. The classical grammar is quite different though, and more complicated.
As a side note, that class was absurdly easy because I already knew almost all the vocabulary. The classical grammar is quite different though, and more complicated.