5.
已知公差不为零的等差数列\(\left\{{a}_{n}\right\} \)中,\({{a}_{3}}=7\),且\({{a}_{1}},{{a}_{4}},{{a}_{13}}\)成等比数列
\((1)\)求数列\(\left\{{a}_{n}\right\} \)的通项公式
\((2)\)令\({{b}_{n}}=\dfrac{1}{{{a}^{2}}_{n}-1}\) \((n∈N^{*})\),求数列\(\left\{{b}_{n}\right\} \)的前\(n\)项和\({{S}_{n}}\)