定义:称\(\dfrac{n}{{{P}_{1}}+{{P}_{2}}+...+{{P}_{n}}}\)为\(n\)个正数\(P_{1}\),\(P_{2}\),\(…P_{n}\)的“均倒数”,已知数列\(\{a_{n}\}\)的前\(n\)项的“均倒数”为\(\dfrac{1}{n+2}\).
\((1)\)求\(\{a_{n}\}\)的通项公式;
\((2)\)设\({{c}_{n}}=\dfrac{{{a}_{n}}}{{{3}^{n}}}\),试判断并说明数列\(\{c_{n}\}\)的单调性;
\((3)\)求数列\(\{c_{n}\}\)的前\(n\)项和\(T_{n}\).