共50条信息
已知等比数列\(\{a_{n}\}\)的公比\(q > 1\),\(a_{1}=1\),且\(2a_{2}\),\(a_{4}\),\(3a_{3}\)成等差数列.
\((1)\)求数列\(\{a_{n}\}\)的通项公式;
\((2)\)记\(b_{n}=2na_{n}\),求数列\(\{b_{n}\}\)的前\(n\)项和\(T_{n}\).
等差数列\(\left\{ {{a}_{n}} \right\}\)中,\({{a}_{3}}=4\),前\(11\)项的和\(S_{11}=110\)则\(a_{9}=\)
设正项等比数列\(\{{a}_{n}\} \)的前\(n \)项和为\({{S}_{n}}\),若\(S_{3}=3\),\(S_{9}-S_{6}=12\),则\(S_{6}=\) .
设数列\(\left\{ {{a}_{n}} \right\}\)满足对任意的\(n\in {{N}^{*}}\),\({{P}_{n}}\left( n,{{a}_{n}} \right)\)满足\(\overrightarrow{{{P}_{n}}{{P}_{n+1}}}=(1,2)\),且\({{a}_{1}}+{{a}_{2}}=4\),则数列\(\left\{ \dfrac{1}{{{a}_{n}}\cdot {{a}_{n+1}}} \right\}\)的前\(n\)项的和\({{S}_{n}}\)为_________.
黑白两种颜色的正六边形地面砖按如图的规律拼成若干个图案:则第\(n\)个图案中有白色地面砖 块\(.\)
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