13. (1-log-14)(1 – log214)

13. (1 - log₇14)(1 - log₂14)

(1 - log₇14)(1 - log₂14) = (1 - (log₇7 + log₇2))(1 - (log₂7 + log₂2)) = (1 - (1 + log₇2))(1 - (log₂7 + 1)) = (-log₇2)(-log₂7) = log₇2 * log₂7

Применим свойство логарифма: logₐb ⋅ logbc = logₐc

log₇2 * log₂7 = log₇7 = 1

Ответ: 1