等差数列an,Sn=n^2-4n+1,求a1的绝对值+a2的绝对值+.a10的绝对值

{an}是等差数列,Sn=n2-2n,求：an 已知等差数列an中,a1=1,前n项和Sn,若S(n+1)/Sn=(4n+2)/(n+1),求an 已知等差数列an中,a1=1,前n项和Sn,若S(n+1)/Sn=(4n+2)/(n+1),求an an是等差数列,求​lim (Sn+Sn+1)/(Sn+Sn-1)lim (Sn+Sn+1)/(Sn+Sn-1)=[n(n+1)/2+(n+1)(n+2)/2]/[n(n+1)/2+n(n-1)/2]=(2n²+4n+2)/2n²=1+2/n+1/n²我就想知道第一步怎么来的 等差数列题目S(n+1)/Sn=(n+2)/n,求An 已知等差数列{an}中,an=4^n-1 +n,n属于n,(1)求数列{an}的前n项和sn(2)证明不等式sn+1小于等于4sn,对任意n属于正整数皆成立 已知sn=32n-n^2求等差数列|an|的前n项和sn 数列{an},前n项和sn,a1=2,a1、S(n+1)、4Sn成等差数列,求{an}通项公式、Sn 等差数列{an}a1=1前n项和为Sn且S2n/Sn=4n+2/n+1 (1)求an通项公试 等差数列an中,a1=1前n项和Sn,满足条件S2n/Sn=4n+2/n+1,求an通项 等差数列an=4n-16,求Sn最小值 设Sn是等差数列an的前n项和,a5=2,an-4=30(n≥5,n∈N*),Sn=136,求n 等差数列{an}前n项和为Sn=3n-2n^2,求an 数列an ,a1=1,前n项和为Sn ,正整数n对应的n an Sn 成等差数列.1.证明{Sn+n+2}成等比数列,2.求{n+2/n(n+1)(1+an)}前n项和 等差数列前几项和SnTn,Sn/Tn=2n/3n+1求an/bn 等差数列an=2n-1,求数列{1/an*a n+1}的前n项和Sn 已知等差数列{an}的前n项和为Sn,且（2n-1)Sn+1-(2n+1)Sn=4n^2-1(n属于正整数）求数列{an}的通项公式 已知一等差数列{an}的前n项和Sn=n^2-3n+1,求an