(r + 5)7 - 54 = (r + 5)4
7r + 35 - 54 = 4r + 20
7r - 19 = 4r + 20
7r - 4r = 20 + 19
3r = 39
r = 13
Проверка:
(13 + 5)7 - 54 = (13 + 5)4
187 - 54 = 184
126 - 54 = 72
72 = 72
Ответ: r = 13
(r + 5)7 - 54 = (r + 5)4
7r + 35 - 54 = 4r + 20
7r + 35 - 54 = 4r + 20
7r - 19 = 4r + 20
7r - 4r = 20 + 19
3r = 39
r = 13
Проверка:
(13 + 5)7 - 54 = (13 + 5)4
187 - 54 = 184
126 - 54 = 72
72 = 72
Ответ: r = 13