@article{MO_2019_90_2_a1,
     author = {V. I. Voytitsky and A. Sh. Mustafaeva},
     title = {Solution of extremal problems without use of derivative},
     journal = {Matemati\v{c}eskoe obrazovanie},
     pages = {7--19},
     publisher = {mathdoc},
     volume = {90},
     number = {2},
     year = {2019},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MO_2019_90_2_a1/}
}