已知：\(3^x=4,3^{2x-4y}=2,求解：9^y的值。\)
\[
\begin{align*}
& 由已知3^{2x-4y} =2 & \\
& \frac{3^{2x}}{3^{4y}} = 2 \\
& \frac{(3^x)^2}{3^{4y}} = 2 \\
& \frac{4^2}{3^{4y}} =2 \\
& 得: 3^{4y} = 8 \\
& (3^{4y})^2 = 8^2 \\
& 9^{4y} =64 \\
& 9^y = \sqrt[4]{64} \\
& 解得：9^y = 2\sqrt{2} \\
\end{align*}
\]