等差数列sm=70,s2m=300,求s3m

已知{an}是等差数列,前n项和记为Sn,已知数列Sm,求证：Sm,S2m-Sm,S3m-S2m也成等差数列 在等差数列{an}中,公差为d,顺次m项和Sm,S2m-Sm,S3m-S2m,.组成公差为______的等差数列 已知等比数列an中,Sm=10 S2m=30 等差数列中Sm=n,Sn=m,求Sm+n简单方法 等差数列An,Sm=n,Sn=m(m不等于n),求Sm+n 等差数列前n项和Sn Sm=k Sk=m 求Sm+k 等差数列Sm=m/n,Sn=n/m..求Sm+n? 在等差数列中,已知Sm=Sn（m≠n）,求Sm+n的值. 等差数列{an}的前n项和为Sn,已知am-1 +am+1 -(am)^2=0,S2m-1=38,求m 等差数列前n项和{Sn},S8=132,Sm=690,Sm-8=270,求m Sn为等差数列的前n项和,Sn=m,Sm=n,求:Sm+n 等差数列an前n项和为Sn=m,Sm=n,求Sm+n的值