共50条信息
已知数列\(\left\{{a}_{n}\right\} \)满足\({a}_{1}=1 \),\({a}_{n+1}-{a}_{n}\geqslant 2\left(n∈{N}^{*}\right) \),则\((\) \()\)
在等差数列\(\{{{a}_{n}}\}\)中,\({{a}_{2}}+{{a}_{7}}=-23\),\({{a}_{3}}+{{a}_{8}}=-29\).
\((1)\)求数列\(\{{{a}_{n}}\}\)的通项公式;
\((2)\)设数列\(\{{{a}_{n}}+{{b}_{n}}\}\)是首项为\(1\),公比为\(q\)的等比数列,求\(\{{{b}_{n}}\}\)的前\(n\)项和\({{S}_{n}}\).
设\(S_{n}\)是等差数列\(\{a_{n}\}\)的前\(n\)项和,若\( \dfrac{a_{7}}{a_{5}}= \dfrac{9}{13}\),则\( \dfrac{S_{13}}{S_{9}}= (\) \()\)
已知\(S_{n}\)是数列\(\{a_{n}\}\)的前\(n\)项和,且\(S_{n+1}=S_{n}+a_{n}+3\),\(a_{4}+a_{5}=23\),则\(S_{8}=(\) \()\)
已知等差数列\(\{a_{n}\}\)中,公差\(d=2\),\(a_{n}=11\),\(S_{n}=35\),则\(a_{1}=(\) \()\)
已知等差数列\(\{\)\({a}_{n}\)\(\}\)中,若\({S}_{2}\)\(=16\),\({S}_{4}\)\(=24\),求数列\(\{|\)\({a}_{n}\)\(|\}\)的前\(n\)项和\({T}_{n}\).
数列\(1\),\(\dfrac{1}{1+2}\),\(\dfrac{1}{1+2+3}\),\(…\),\(\dfrac{1}{1+2+\ldots +n}\)的前\(n\)项和为( )
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