等差数列{a n}中,前N项和为Sn,首项a1=4,S9=0,求公差d,若an+sn=-10,求n
等差数列{an}中,a1=3,公差d=2,Sn为前n项和,求1S
等差数列{an}前n项和为Sn,且Sn=3n^2+n 求公差d
等差数列{an}中,a1>0,前n项和为Sn,且S9>0,S10
已知公差不为0的等差数列{An}的首项A1=1,前n项和为Sn,若数列{Sn/An}是等差数列,求An?
等比数列{an}的前n项和为sn,若S3,S9,S6成等差数列,求此数列的公差,
已知等差数列{an}的公差d=1+前n项和为sn,若1,a1,a3成等比数列求a1
已知等差数列{an}的公差d=1,前n项和为sn,若1,a1,a3成等比数列求a1
已知Sn为等差数列{an}的前n项之和,S9=18,Sn=256,a(n-4)=30(n〉9),求n
等差数列{an}中,公差d>0,Sn为前n项和,满足a2a3=45,a1+a4=14.求an通项公式,设bn=Sn/n+
已知等差数列an公差d>0,前n项和为sn若s7=s11求当n为何值时sn最小
设a1,d为实数,首项a1,公差为d的等差数列an的前n项和为sn,满足s5s6+15=0,若s5=5求s6及a1,求d
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=( )