ON ONE PROPERTY OF THE NUMERICAL RANGE OF A TWO-PARAMETER SPECTRAL PROBLEM. - Tagi, Mustafayev Sadig; Mammadov, Eldar Sh.; Cumshud, Kasamanli Hamlet; Isfandiyar, Askerova Rada (German International Journal of Modern Science / Deutsche Internationale Zeitschrift für Zeitgenössische Wissenschaft, 2025)