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            • 1.

              有四个数,其中前三个数成等差数列,后三个数成等比数列,并且第一个数与第四个数的和是\(16\),第二个数与第三个数的和是\(12\),求这四个数.

            • 2.

              已知等差数列\(\{{{a}_{n}}\}\)中,公差\(d\ne 0\)\({{S}_{7}}=35\),且\({{a}_{2}}\)\({{a}_{5}}\)\({{a}_{11}}\)成等比数列.

              \((1)\)求数列\(\{{{a}_{n}}\}\)的通项公式;

              \((2)\)若\({{T}_{n}}\)为数列\(\{\dfrac{1}{{{a}_{n}}{{a}_{n+1}}}\}\)的前\(n\)项和,且存在\(n\in {{\mathrm{N}}^{*}}\),使得\({{T}_{n}}-\lambda {{a}_{n+1}}\geqslant 0\)成立,求实数\(\lambda \)的取值范围.

            • 3. 已知\(\{a_{n}\}\)是等差数列,\(\{b_{n}\}\)是等比数列,且\(b_{2}=3\),\(b_{5}=81\),\(a_{1}=b_{1}\),\(a_{14}=b_{4}\).
              \((1)\)求\(\{a_{n}\}\)的通项公式;
              \((2)\)设\(c_{n}=a_{n}+b_{n}\),求数列\(\{c_{n}\}\)的前\(n\)项和.
            • 4.

              已知数列\({ }\!\!\{\!\!{ }{{a}_{n}}{ }\!\!\}\!\!{ }\)是等比数列,数列\(\{{b}_{n}\} \)是等差数列,若\({{a}_{1}}\cdot {{a}_{6}}\cdot {{a}_{11}}=-3\sqrt{3}\),\({{b}_{1}}+{{b}_{6}}+{{b}_{11}}=7\pi \),则\(\tan \dfrac{{{b}_{3}}+{{b}_{9}}}{1-{{a}_{4}}\cdot {{a}_{8}}}\)的值是

              A.\(1\)                                
              B.\(\dfrac{\sqrt{2}}{2}\)
              C.\(-\dfrac{\sqrt{2}}{2}\)
              D.\(-\sqrt{3}\)
            • 5.

              设数列\(\{a_{n}\}\)的前\(n\)项和\(S_{n}\)满足:\({{S}_{n}}={{n}^{2}}+1\),等比数列\(\{b_{n}\}\)满足:\(b_{2}=2\),\(b_{5}=16\)

              \((1)\)求数列\(\{a_{n}\}\),\(\{b_{n}\}\)的通项公式;

              \((2)\)求数列\(\{a_{n}b_{n}\}\)的前\(n\)项和\(T_{n}\).

            • 6.

              若数列\(x\),\(a_{1}\),\(a_{2}\),\(y\)成等差数列,\(x\),\(b_{1}\),\(b_{2}\),\(y\)成等比数列,则\( \dfrac{(a_{1}+a_{2})^{2}}{b_{1}·b_{2}}\)的取值范围是\((\)  \()\)

              A.\((-∞,-2]\) 

              B.\((-∞,0]\)

              C.\([4,+∞)\) 

              D.\((-∞,0]\)或\([4,+∞)\)
            • 7. 在数列\(\{a_{n}\}\)中,已知\(a_{1}=2\),\(a_{2}=7\),\(a_{n+2}\)等于\(a_{n}a_{n+1}(n∈N^{*})\)的个位数,则\(a_{2013}\)的值是\((\)  \()\)
              A.\(8\)
              B.\(6\)
              C.\(4\)
              D.\(2\)
            • 8.

              已知\({数列}\{ a_{n}\}\)的前\(n\)项\({和}{为}A_{n}\),对\({任意}n{∈}N^{{*}}{满足}\dfrac{A_{n{+}1}}{n{+}1}{-}\dfrac{A_{n}}{n}{=}\dfrac{1}{2}{,}{且}a_{1}{=}1\),\({数列}\{ b_{n}\}{满}{足}b_{n{+}2}{-}2b_{n{+}1}{+}b_{n}{=}0(n{∈}N{*}){,}b_{3}{=}5\),其前\(9\)项和为\(63{.}(1)\)求\({数列}\{ a_{n}\}{和}\{ b_{n}\}\)的通项公式\({;}(2){令}c_{n}{=}\dfrac{b_{n}}{a_{n}}{+}\dfrac{a_{n}}{b_{n}}\),\({数列}\{ c_{n}\}\)的前\(n\)项\({和}{为}T_{n}\),若对任意正整数\(n\),\({都}{有}T_{n}{\geqslant }2n{+}a\),求实数\(a\)的取值范围\({;}(3)\)将\({数列}\{ a_{n}\}{,}\{ b_{n}\}\)的项按照“当\(n\)为奇数\({时}{,}a_{n}\)放在前面;当\(n\)为偶数\({时}{,}b_{n}\)放在前面”的要求进行“交叉排列”,得到一个新的数列:\({\ \ \ \ \ \ \ \ \ \ \ \ \ \ a}_{1}{,}b_{1}{,}b_{2}{,}a_{2}{,}a_{3}{,}b_{3}{,}b_{4}{,}a_{4}{,}a_{5}{,}b_{5}{,}b_{6}{,…}\),

              求这个新数列的前\(n{项}{和}S_{n}\).
            • 9. 定义运算符号“\(\prod \)”:表示若干个数相乘,例如:\(=1×2×3×…×n.\)记\(T_{n}=\),其中\(a_{i}\)为数列\(\{a_{n}\}\)中的第\(i\)项.
              \((1)\)若\(a_{n}=2n-1\),则\(T_{4}=\)____________;
              \((2)\)若\(T_{n}=n^{2}(n∈N^{*})\),则\(a_{n}=\)____________.
            • 10.

              已知\(\{{a}_{n}\} \)为等差数列,前\(n\)项和为\({S}_{n}(n∈{N}^{*}) \),\(\{{b}_{n}\} \)是首项为\(2\)的等比数列,且公比大于\(0\),

              \((1)\)求的通项公式;

              \((2)\)求数列\({a}_{2n}{b}_{2n-1} \)的前\(n\)项和\((n∈{N}^{*}) \) .

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