\((1)\)已知数列\(\{{{a}_{n}}\}\)为等差数列，且\({{a}_{1}}+{{a}_{5}}+{{a}_{9}}=\dfrac{\pi }{4}\)，求\(\sin ({{a}_{4}}+{{a}_{6}}+\dfrac{3}{2}\pi )\)的值；

\((2)\)已知数列\(\{{{a}_{n}}\}\)为等差数列，且满足\({{a}_{1}}+{{a}_{2}}+{{a}_{5}}=26\)，\(a_{2}^{2}={{a}_{1}}{{a}_{5}}\)，求\(\{{{a}_{n}}\}\)的通项．