共50条信息
已知数列\(\{a_{n}\}\)中,\(a_{1}=1\),\({{a}_{n+1}}=\dfrac{2{{a}_{n}}}{2+a}(n\in {{N}_{+}})\).
\((\)Ⅰ\()\)求\(a_{2}\),\(a_{3}\),\(a_{4}\)的值,猜想数列\(\{a_{n}\}\)的通项公式;
\((\)Ⅱ\()\)运用\((\)Ⅰ\()\)中的猜想,写出用三段论证明数列\(\{\dfrac{1}{{{a}_{n}}}\}\)是等差数列时的大前提、小前提和结论.
已知数列\(\left\{{a}_{n}\right\} \)中,\({a}_{1}=1,{a}_{2}=4,2{a}_{n}={a}_{n-1}+{a}_{n+1}(n\geqslant 2,n∈{N}^{*}) \) ,当\({a}_{n}=301 \)时,序号\(n= (\) \()\)
南北朝时期的数学古籍\(《\)张邱建算经\(》\)有如下一道题:“今有十等人,每等一人,宫赐金以等次差\((\)即等差\()\)降之,上三人,得金四斤,持出;下四人后入得三斤,持出;中间三人未到者,亦依等次更给\(.\)问:每等人比下等人多得几斤?”( )
已知数列是等差数列,且\(a\)\({\,\!}_{1}=1\),\(a\)\({\,\!}_{2}=5\).
\((\)Ⅰ\()\)求数列\(\left\{{a}_{n}\right\} \)的前\(n\)项和\(S_{n}\);
\((\)Ⅱ\()\)在\((\)Ⅰ\()\)中,设\(b_{n}\)\(= \dfrac{{S}_{n}}{n+c} \),求证:当\(c\)\(=- \dfrac{1}{2} \)时,数列\(\left\{{b}_{n}\right\} \)是等差数列.
数列\({a_{n}}\)满足\(a_{1}=1\),\(na_{n+1}=(n+1)a_{n}+n(n+1)\),\(n∈N*\).
\((1)\)证明:数列\(\{\dfrac{{{a}_{n}}}{n}\}\)是等差数列;
\((2)\)设\({{b}_{n}}={{3}^{n}}\sqrt{{{a}_{n}}}\),求数列\({b_{n}}\)的前\(n\)项和\(S_{n}\).
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