题型:解答题 题类:其他 难易度:较易
年份:2018
正项数列\(\left\{ {{a}_{n}} \right\}\)中,\({{a}_{1}}=1\),奇数项\(a_{1}\),\(a_{3}\),\(a_{5}....a_{2k-1}....\)构成公差为\(d\)的等差数列,偶数项\(a_{2}\),\(a_{4}\),\(a_{6}\),\(....\),\(a_{2k}\),\(...\)构成公比\(q=2\)的等比数列,且\(a\)\({\,\!}_{1}\),\(a\)\({\,\!}_{2}\),\(a\)\({\,\!}_{3}\)成等比数列, \(a\)\({\,\!}_{4}\),\(a\)\({\,\!}_{5}\),\(a\)\({\,\!}_{7}\)成等差数列.
\((\)Ⅰ\()\)求\({{a}_{2}}\)和\(d\);
\((\)Ⅱ\()\)求数列\(\left\{ {{a}_{n}} \right\}\)的前\(2n\)项和\({{S}_{2n}}\).