Trigonometric Number

In mathematics, a trigonometric number is an irrational number produced by taking the sine or cosine of a rational multiple of a circle, or equivalently, the sine or cosine in radians of a rational multiple of π, or the cosine of a rational number of degrees.

Ivan Niven gave proofs of theorems regarding these numbers in Numbers: Rational and Irrational published in 1961. Li Zhou and Lubomir Markov recently improved and simplified Niven's proofs in the book.

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