已知数列an的前n项和Sn=n^2-9n,第k项满足5
已知数列an的前n项和Sn=n^2-9n,第k项满足5
已知数列{an}的前n项和Sn=n^2-9n 第K项满足5
已知数列{An }的前 n项和Sn=nxn-9n ,第 k项满足5
已知数列{an}的前n项和Sn=n^2-9n,第k项满足5<ak<8,则k等于
已知数列{An}的前n项和Sn=n平方-9n,第k项满足5<Ak<8,则k等于
已知数列an前n项和Sn=n^2-9n,第k项满足5<ak<8,则k等于多少
已知数列{An}的前n项和Sn等于n平方减9n,第k项满足5<Ak
已知数列{an}满足ak+a(n-k)=2,(k,n-k∈N*),则数列{an}的前n项和Sn=
已知数列{an}的前n项和Sn=n^2-9n,则其通项an=多少;若它的第k项满足5<ak<8,则k=多少
已知数列{an}满足an=2n/3^n,求此数列的前n项和sn
已知数列{an}的前n项和Sn=n2 +2n,第m项满足15
数列an的前n项和Sn满足:Sn=2an-3n