Kozhanov, A., Koshanov, B., Sultangaziyeva, Z., Yemir Kady oglu, A., & Smatova, G. (2020). Spectral problem for the sixth order nonclassical differential equations. Bulletin of the Karaganda University. Mathematics Series, 97(1), 79–86. https://doi.org/10.31489/2020m1/79-86