1.d=2 An=11 Sn=35 求n=?2.S9=-24 a1=-8 则d=?3.数列a,a,a,...的前n项和Sn=?4.在等差数列｛An｝中,a3=12,S12大于0,S13小于0,求公差d的取值范围.

等差数列AN中D=2 ,AN=11,SN=35 求A1与N? an=n*2^n,求Sn an=2^n+n,求Sn 已知数列{an}的前n项的和Sn=n^2+5n-1求通项公式在等差数列{an}中,已知d=2,an=11 Sn=35,求an和n 在等差数列{an}中,公差d=2,an=11,Sn=35,求a1和项数n 在等差数列an中已知d=2,an=11,sn=35求a1和n的值 sn=2*3^n,求an 等差数列｛an｝前n项和为Sn,且Sn=3n^2+n 求公差d a1=1/2,Sn=n^2an-n(n-1),求Sn和an Sn=n平方-n.求an an=n(n+1) 求sn 在等差数列中,已知d=2,an=1,sn=8求an,n 等差数列{an}中,d=2,n=5,an=-10,求a1及Sn a1=1,Sn=n^2an,求an 知数列Sn=2An-2n求An 已知Sn=n^2+an/2 求an {an}是等差数列,Sn=n2-2n,求：an Sn=2an+(-1)n次方 怎么求an