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\(a+b=\)
进入组卷