log 2 15 - log 2 30 =

Используем свойство логарифмов: logₐ b - logₐ c = logₐ (b/c). log₂ 15 - log₂ 30 = log₂ (15/30) = log₂ (1/2) = log₂ (2⁻¹) = -1