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  • 题型:解答题 题类:历年真题 难易度:较易

    年份:2018

    已知等差数列\(\{a_{n}\}\)的前\(n\)项和味\(S_{n}\),\(a_{1} > 0\),\(a_{1}⋅a_{2}= \dfrac {3}{2}\),\(S_{5}=10\).
    \((1)\)求数列\(\{a_{n}\}\)的通项公式;
    \((2)\)记数列\(b_{n}= \begin{cases} \overset{2^{a_{n}},n{为奇数}}{a_{n},n{为偶数}}\end{cases}\),求数\(\{b_{n}\}\)的前\(2n+1\)项和\(T_{2n+1}\).
  • 题型:解答题 题类:历年真题 难易度:较易

    年份:2018

    已知数列\(\{a_{n}\}\)是等差数列,且\(a_{1}\),\(a_{2}(a_{1} < a_{2})\)分别为方程\(x^{2}-6x+5=0\)的两个实数根.

    \((1)\)求数列\(\{a_{n}\}\)的前\(n\)项和\(S_{n}\);

    \((2)\)设\({{b}_{n}}=\dfrac{{{S}_{n}}}{n+c}\),求证:当\(c=-\dfrac{1}{2}\)时,数列\(\{b_{n}\}\)是等差数列.

  • 题型:解答题 题类:历年真题 难易度:较易

    年份:2018

    已知公差不为零的等差数列\(\{a_{n}\}\)满足\(a_{1}=5\),且\(a_{3}\),\(a_{6}\),\(a_{11}\)成等比数列.
    \((1)\)求数列\(\{a_{n}\}\)的通项公式;
    \((2)\)设\(b_{n}=a_{n}\cdot 3^{n-1}\),求数列\(\{b_{n}\}\)的前\(n\)项和\(S_{n}\).
  • 题型:解答题 题类:历年真题 难易度:较易

    年份:2018

    已知数列\(\{a_{n}\}\)是各项均不为\(0\)的等差数列,公差为\(d\),\(S_{n}\)为其前\(n\)项和,且满足\(a_{n}^{2}=S_{2n-1}\),\(n∈N^{*}.\)数列\(\{b_{n}\}\)满足\(b_{n}= \dfrac {1}{a_{n}a_{n+1}}\),\(T_{n}\)为数列\(\{b_{n}\}\)的前\(n\)项和.
    \((1)\)求数列\(\{a_{n}\}\)的通项公式和\(T_{n}\);
    \((2)\)是否存在正整数\(m\),\(n(1 < m < n)\),使得\(T_{1}\),\(T_{m}\),\(T_{n}\)成等比数列?若存在,求出所有\(m\),\(n\)的值;若不存在,请说明理由.