3.
已知等差数列\(\{a_{n}\}\)的公差\(d\neq 0\),其前\(n\)项和为\(S_{n}\),若\(a_{2}+a_{8}=22\),且\(a_{4}\),\(a_{7}\),\(a_{12}\)成等比数列.
\((\)Ⅰ\()\)求数列\(\{a_{n}\}\)的通项公式;
\((\)Ⅱ\()\)若\(T_{n}= \dfrac {1}{S_{1}}+ \dfrac {1}{S_{2}}+…+ \dfrac {1}{S_{n}}\),证明:\(T_{n} < \dfrac {3}{4}\)