已知等差数列{an}中,a1=29,S10=S20,问这个数列的前多少项和最大?并求此最大值.

已知等差数列{an}中,a1 已知等差数列an中,a1 等比数列{an}中,前n项和为sn,已知S1,S3,S2成等差数列,求{an}的公比Q.已知a1-a3=3,求sn? 等比数列{an}中,前n项和为sn,已知S1,S3,S2成等差数列,求{an}的公比Q.已知a1-a3=3,求sn?RT. 已知等差数列{an}中,a1=2.an+1=an+3分之an 求an 已知等差数列{an}中,S10=120,a1+a10等于 已知数列｛an｝中,a1=1,且Sn,Sn+1,2S1成等差数列,用数学归纳法证明Sn=(2^n-1)/2^(n-1) 等差数列{An}中,a1 等差数列{an}中,a1 等差数列{an}中,a1 等差数列{An}中,a1 等差数列{An}中,A1 等差数列an中,a1 等差数列{an}中,a1 等差数列{an}中,a1 等差数列an中,a1 等差数列{an}中,a1 S1,S2,S3成等差数列求{an}的公比Q.已知a1-a3=3,求sn