$$log_{\frac{1}{\sqrt{2}}} 128\sqrt{2} = log_{2^{-\frac{1}{2}}} (2^7 \cdot 2^{\frac{1}{2}}) = log_{2^{-\frac{1}{2}}} 2^{\frac{15}{2}} = \frac{\frac{15}{2}}{-\frac{1}{2}} = -15$$
Ответ: -15