共50条信息
设等比数列\(\{{{a}_{n}}\}\)的公比\(q=2\),前\(n\)项和为\({{S}_{n}}\),则\(\dfrac{{{S}_{4}}}{{{a}_{2}}}=\) \((\) \()\)
在等比数列\(\{a_{n}\}\)中,公比\(q=2\),前\(87\)项和\(S_{87}=140\),则\(a_{3}+a_{6}+a_{9}+…+a_{87}\)等于\((\) \()\)
等比数列\(\{ a_{n}\}\)前四项和为\(1\),前\(8\)项和为\(17\),则它的公比为\(({ })\)
已知数列\(\{a_{n}\}\)是以\(a\)为首项,\(b\)为公比的等比数列,数列\(\{b_{n}\}\)满足\(b_{n}=1+a_{1}+a_{2}+…+a_{n}(n=1,2,…)\),数列\(\{c_{n}\}\)满足\(c_{n}=2+b_{1}+b_{2}+…+b_{n}(n=1,2,…)\),若\(\{c_{n}\}\)为等比数列,则\(a+b=\)
设等比数列\(\{a_{n}\}\)的公比为\(q(q\neq 1)\),则数列\(a_{3}\),\(a_{6}\),\(a_{9}\),\(…\),\(a_{3n}\),\(…\)的前\(n\)项和为\((\) \()\)
数列\(1\),\((1+2)\),\((1+2+{{2}^{2}})\),\(.......\),\((1+2+{{2}^{2}}+{{2}^{3}}+\cdots +{{2}^{n-1}})\)的前\(n\)项和是( )
设等比数列\(\{{{a}_{n}}\}\)的前\(n\)项和为\({{S}_{n}}\),则“\({{a}_{1}} > 0\)”是“\({{S}_{3}} > {{S}_{2}}\)”的\((\) \()\)
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