lg (log2 (log7 x))=0

lg (log₂ (log₇ x))=0
ОДЗ: х > 0
log₂ (log₇x) = 10⁰
log₂ (log₇x) = 1
log₇x = 2¹
log₇x = 2
x = 7²
x = 49

Ответ: 49