Find the general term of the geometric sequences defined as follows.
4, \dfrac{-8}{3},\dfrac{16}{9},\dfrac{-32}{27},\dfrac{64}{81}, …
2, 6, 18, 54, 162, ...
6, -\dfrac{9}{2}, \dfrac{27}{8}, -\dfrac{81}{32},...
\dfrac{1}{2}, \dfrac{1}{4}, \dfrac{1}{8}, \dfrac{1}{16},\dfrac{1}{32}...
6, -12, 24, -48, 96,...
-4,-5,-\dfrac{25}{4},-\dfrac{125}{16},...
27, 18, 12, 8, \dfrac{16}{3},...