11. Igx-lg11=lg19-1g(30-x)

Решим уравнение lgx - lg11 = lg19 - lg(30-x)

lgx + lg(30-x) = lg19 + lg11

lg(x(30-x)) = lg(19*11)

30x - x² = 209

x² - 30x + 209 = 0

x = (30 +- sqrt(30² - 4*209))/2 = (30 +- sqrt(900 - 836))/2 = (30 +- sqrt(64))/2 = (30 +- 8)/2

x = 19 или x = 11

Ответ: 11, 19