System of equations; 3 equations - 2-nd degree

[ins-]

nnosipov в сообщении #1477852 писал(а):

What is the mentioned Modenov's book?

It is the Modenov's book: https://edu-lib.com/matematika-2/dlya-s ... o-spetsial
"Сборник задач по специальному курсу элементарной математики" - Моденов П.С.

[nnosipov]

ins-
Thank you.