@article{UM_1997_5_3_a4,
     author = {Calda, Emil},
     title = {Heron\r{u}v vzorec a kosinova v\v{e}ta},
     journal = {U\v{c}itel matematiky},
     pages = {157--159},
     year = {1997},
     volume = {5},
     number = {3},
     language = {cs},
     url = {http://geodesic.mathdoc.fr/item/UM_1997_5_3_a4/}
}