设等差数列〔An〕的前n项和为Sn,若S九=36,则a二+a五+a八=?
设等差数列〔An〕的前n项和为Sn,若S九=36,则a二+a五+a八=?
设Sn为等差数列{an}的前n项和,S7=42,Sn=510,若a(n-3)=45(n>7),则n等于
已知{(an}是等差数列,d为公差且不为0,a1和d均为实数,它的前n项和记作Sn,设集合A={〔an,Sn/n〕︱n∈
设等比数列 {an} 的公比为q,前n项和为Sn,若S(n+1),Sn,S(n+2)成等差数列,则q=
设数列【an】的前n项和Sn=a^n-1,a≠0,试判定【an】能否为等差数列,能否为等比数列
已知数列an的前n项和为sn=5/6n(n+3),1:求证an为等差数列 2:设bn=a3n+a
设数列{an}的前n项和为Sn,Sn=a
设Sn是等差数列{an}的前n项和,若a
设数列 an 的前n项和为Sn,a1=1,an=Sn/n+2(n-1)(n∈N*) 求证:数列{an}为等差数列,并求a
设数列{an}的前n项和为Sn,其中an不等于0.a1为常数,且-a1,Sn,a(n+1)成等差数列,设Bn=1-Sn,
设Sn为等差数列{an}的前n项和,若a1=1,公差d=2,Sn+2-Sn=36,则n=( )
已知等差数列(an)的前n项和为Sn,且a3=5,S15=225,设bn=2^a n+2n,求数