$$ \frac{a^{21} \cdot b^4}{(a \cdot b)^{16}} = \frac{a^{21} \cdot b^4}{a^{16} \cdot b^{16}} = a^{21-16} \cdot b^{4-16} = a^5 \cdot b^{-12} = \frac{a^5}{b^{12}} $$
При $$a=2$$ и $$b=\sqrt{2}$$:
$$ \frac{2^5}{(\sqrt{2})^{12}} = \frac{32}{(2^{1/2})^{12}} = \frac{32}{2^6} = \frac{32}{64} = \frac{1}{2} $$
Ответ: 0.5