\(\dfrac{16}{81}=\left(\dfrac{2}{3}\right)^4\)
\(\dfrac{16}{81}=\left(-\dfrac{4}{9}\right)^2\)
\(\dfrac{16}{81}=\left(\dfrac{2}{3}\right)^4\)
\(\Rightarrow\left[{}\begin{matrix}\dfrac{16}{81}=\left(\dfrac{-4}{9}\right)^2\\\dfrac{16}{81}=\left(\dfrac{-2}{3}\right)^4\\\dfrac{16}{81}=\left(\dfrac{2}{3}\right)^4\end{matrix}\right.\)