Using Euler’s theorem, geometric sums and Chebyshev polynomials, we prove trigonometric identities involving sums and multiplications of cosine.
"Partial Sum Trigonometric Identities and Chebyshev Polynomials,"
Rose-Hulman Undergraduate Mathematics Journal: Vol. 19
, Article 5.
Available at: https://scholar.rose-hulman.edu/rhumj/vol19/iss1/5