Use each possible method, to solve:
$ T(n) = T(n/9) + T(8n/9) + n$
$ T(n) = T(2n/3) + 1$
$ T(n) = T(\sqrt{n}) + 1$ (hint: substitute $ n$ by $ 2^k$ )
$ T(n) = 2T(\sqrt{n}) + n$ (hint: substitute $ n$ by $ 2^k$ )
$ T(n) = \sqrt{n}T(\sqrt{n}) + n$ (harder exercise. hint: substitute $ n$ by $ 2^k$ )