B) lg² x – 2 lg x + 4 = 9/lg100x ;

lg² x – 2 lg x + 4 = 9/lg100x

lg² x – 2 lg x + 4 = 9/(lg100 + lgx)

lg² x – 2 lg x + 4 = 9/(2 + lgx)

Пусть t = lg x, тогда:

t² - 2t + 4 = 9/(2 + t)

(t² - 2t + 4)(2 + t) = 9

2t² - 4t + 8 + t³ - 2t² + 4t = 9

t³ = 1

t = 1

lg x = 1

x = 10

Ответ: 10