已知等差数列{An}的前n项和记为Sn,a5=15,a10=25 1.通项An 2.若Sn=112,求n
已知等差数列an满足a3=7,a5+a7=26,an的前n项和为sn.1.求an和sn
已知{An}为等差数列,其前n项和为Sn.若A4+A7+A10=18,A4+A5+...+A14=77且An=13
已知等差数列{an}前n项和为Sn,(1)若Sn=(-1)^n+1*n,求a5+a6及an
等差数列an中,公差d>0,且a5+a10=0,记数列-2/an的前n项和为Sn,则使Sn
已知等差数列{an},a3=7.a5+a7=26.{an}的前n项和为Sn.1.求a4及Sn.
等差数列{an}的前n项和为Sn,且a10=30,a20=50 (1)求通项an(2)若Sn=242求n
已知等差数列{an}前n项和为Sn,若a4=18-a5,S8等于
已知等差数列{an}满足:a3=7,a5+a7=26,{an}的前n项和为Sn.求an及Sn.
已知等差数列{An}前n项的和Sn,若Sm/Sn=m²/n²,则a5/a6
已知等差数列{an}的前n项和记为Sn.已知a10=30,a20=50.求通项an;若Sn等242,求n
1.已知等差数列{an}的前n项和为sn,若a5=18-a4,则s8等于?
已知数列 an等差数列,前N项和记为Sn,a5=负13 S4=负82 求S6,求Sn的最小值