题型:解答题 题类:期中考试 难易度:较易
新
已知数列\(\left\{{{a}_{n}}\right\}\)的首项为\(2\),前\(n\)项和为\({{S}_{n}}\),且\({{a}_{n\text{+}1}}\text{=}{{S}_{n}}+2(n\in{{N}^{*}}).\)
\((1)\)求数列\(\left\{{{a}_{n}}\right\}\)的通项公式;
\((2)\)在\({{a}_{n}}\)与\({{a}_{n\text{+}1}}\)之间插入\(n\)个数,使这\(n\text{+}2\)个数组成一个公差为\({{d}_{n}}\)的等差数列,求证:\(\dfrac{1}{{d}_{1}}{\rm+}\dfrac{1}{{d}_{2}}+\dfrac{1}{{d}_{3}}+⋯+\dfrac{1}{{d}_{n}}< 3.\)