Kanguzhin, B. E., G. Auzerkhan, and M. G. Tastanov. “THE METHOD OF VARIATION OF ARBITRARY CONSTANTS IN THE CASE OF A SYSTEM OF LINEAR DIFFERENTIAL EQUATIONS OF DIFFERENT ORDERS”. Journal of Mathematics, Mechanics and Computer Science, vol. 111, no. 3, Oct. 2021, pp. 16-27, doi:10.26577/JMMCS.2021.v111.i3.02.