<a href="https://doi.org/10.53656/math2021-3-9-res" target="_blank" rel="noopener noreferrer">https://doi.org/10.53656/math2021-3-9-res</a> <span style="color: #ff0000;"><a style="color: #ff0000;" href="https://azbuki.bg/wp-content/uploads/2021/06/Pages-from-Matematika_03_2021_Resheniq-2-21.pdf" target="_blank" rel="noopener noreferrer">Отвори пълния текст</a></span>
