题型:解答题 题类:期中考试 难易度:中档
年份:2018
数列\(\{{{a}_{n}}\}\)的前\(n\)项和为\({{S}_{n}}\),且\({{a}_{n}}\)是\({{S}_{n}}\)和\(1\)的等差中项,等差数列\(\{{{b}_{n}}\}\)满足\({{b}_{1}}={{a}_{1}}\),\({{b}_{4}}={{S}_{3}}\).
\((\)Ⅰ\()\)求数列\(\{{{a}_{n}}\}\)、\(\{{{b}_{n}}\}\)的通项公式;
\((\)Ⅱ\()\)设\({{c}_{n}}=\dfrac{1}{{{b}_{n}}{{b}_{n+1}}}\),数列\(\{{{c}_{n}}\}\)的前\(n\)项和为\({{T}_{n}}\),证明:\(\dfrac{1}{3}\leqslant {{T}_{n}} < \dfrac{1}{2}\).