已知等差数列前三项为a,4,3a,前n项和为Sn,Sk=2550.求1/S1+1/S2+……+1/Sn
首项为3,公差为2的等差数列,Sk为前K项的和求S=1/S1+1/S2+...+1/Sn的和
an=3n,Sn为前n项和,求1/S1+1/S2+1/S3+…+1/Sn.
设数列{an}前n项和为Sn,已知(1/S1)+(1/S2)+.+(1/Sn)=n/(n+1),求S1,S2及Sn
已知等差数列前三项依次为a,4,3a,前n项的和为Sn,且Sk=930,求a及k的值.
数列an是首项为3公差为2的等差数列其前n项和为Sn求An=1/S1+1/S2+1/S3+...+1/Sn
等比数列首项为a,公比为q,Sn前n项和,求S1+S2+……+Sn
已知等差数列{an}的前三项为a-1,4,2a,记其前n项和为Sn,(1)设Sk=2550,求a和k的值,
等差数列前n项和Sn=(-1)^nAn-1/2^n 求 S1+S2+S3+……+S100
设Sn是公差不为0的等差数列an的前n项和,且S1,S2,S4成等比数列.(1)求a
等比数列{an}的前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}的前n项和为Sn已知S1,S3,S2成等差数列,(1)求{an}的公比q(2)若a1-a3=3,求Sn
等比数列{an}的前n项和为Sn,已知S1,S3,S2成等差数列.①求公比q②a1-a3=3,求Sn