13. (1 – logg 18)(1 – log218)

(1 – log₉18)(1 – log₂18) = (1 - (log₉9 + log₉2)) * (1 - (log₂2 + log₂9)) = (1 - (1 + log₉2)) * (1 - (1 + log₂9)) = -log₉2 * (-log₂9) = log₉2 * log₂9 = log₉2 * log₂(3²) = log₉2 * 2log₂3 = log₃²2 * 2log₂3 = (1/2)log₃2 * 2log₂3 = log₃2 * log₂3 = 1

Ответ: 1