@article{10_14708_cm_v23i1_6051,
     author = {S. Tymowski},
     title = {On the analogue of the formula cos \(t = \frac{1}{2} e^{it} + \frac{1}{2} e^{-it}\) for operator cosine functions},
     journal = {Commentationes Mathematicae},
     pages = { 173--182},
     publisher = {mathdoc},
     volume = {23},
     number = {1},
     year = {1983},
     doi = {10.14708/cm.v23i1.6051},
     language = {pl},
     url = {http://geodesic.mathdoc.fr/articles/10.14708/cm.v23i1.6051/}
}