Tymowski, Sławomir On the analogue of the formula \(\cos t = e^{it} + e^{-it}\) for operator cosine functions. (English) Zbl 0594.47035 Ann. Soc. Math. Pol., Ser. I, Commentat. Math. 23, 173-182 (1983). Summary: The aim of this paper is to present some connections between one parameter strongly continuous groups of linear bounded operators on a Banach space and operator cosine functions. We get a formula which is analogous to the classical one: \(\cos t = e^{it}+e^{-it}\). Cited in 1 Document MSC: 47D03 Groups and semigroups of linear operators 47D99 Groups and semigroups of linear operators, their generalizations and applications Keywords:one parameter strongly continuous groups of linear bounded; operators on a Banach space; operator cosine functions; one parameter strongly continuous groups of linear bounded operators on a Banach space PDFBibTeX XMLCite \textit{S. Tymowski}, Ann. Soc. Math. Pol., Ser. I, Commentat. Math. 23, 173--182 (1983; Zbl 0594.47035)