3道等比数列的题目,1.设等差数列{an}的前n项和为sn,若s6/s4=1/4,求s9/s32.设数列{an}的前n项和为sn,sn-2sn-1=2(n大于或等于2),a1=2(1)求证:数列{sn+2}是等比数列 (2)求sn (3)求an3.s6=9,s2=4,则s4=
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![3道等比数列的题目,1.设等差数列{an}的前n项和为sn,若s6/s4=1/4,求s9/s32.设数列{an}的前n项和为sn,sn-2sn-1=2(n大于或等于2),a1=2(1)求证:数列{sn+2}是等比数列 (2)求sn (3)求an3.s6=9,s2=4,则s4=](/uploads/image/z/11037924-36-4.jpg?t=3%E9%81%93%E7%AD%89%E6%AF%94%E6%95%B0%E5%88%97%E7%9A%84%E9%A2%98%E7%9B%AE%2C1.%E8%AE%BE%E7%AD%89%E5%B7%AE%E6%95%B0%E5%88%97%7Ban%7D%E7%9A%84%E5%89%8Dn%E9%A1%B9%E5%92%8C%E4%B8%BAsn%2C%E8%8B%A5s6%2Fs4%3D1%2F4%2C%E6%B1%82s9%2Fs32.%E8%AE%BE%E6%95%B0%E5%88%97%7Ban%7D%E7%9A%84%E5%89%8Dn%E9%A1%B9%E5%92%8C%E4%B8%BAsn%2Csn-2sn-1%3D2%EF%BC%88n%E5%A4%A7%E4%BA%8E%E6%88%96%E7%AD%89%E4%BA%8E2%EF%BC%89%2Ca1%3D2%EF%BC%881%EF%BC%89%E6%B1%82%E8%AF%81%EF%BC%9A%E6%95%B0%E5%88%97%7Bsn%2B2%7D%E6%98%AF%E7%AD%89%E6%AF%94%E6%95%B0%E5%88%97+%EF%BC%882%EF%BC%89%E6%B1%82sn+%EF%BC%883%EF%BC%89%E6%B1%82an3.s6%3D9%2Cs2%3D4%2C%E5%88%99s4%3D)
3道等比数列的题目,1.设等差数列{an}的前n项和为sn,若s6/s4=1/4,求s9/s32.设数列{an}的前n项和为sn,sn-2sn-1=2(n大于或等于2),a1=2(1)求证:数列{sn+2}是等比数列 (2)求sn (3)求an3.s6=9,s2=4,则s4=
3道等比数列的题目,
1.设等差数列{an}的前n项和为sn,若s6/s4=1/4,求s9/s3
2.设数列{an}的前n项和为sn,sn-2sn-1=2(n大于或等于2),a1=2
(1)求证:数列{sn+2}是等比数列 (2)求sn (3)求an
3.s6=9,s2=4,则s4=
3道等比数列的题目,1.设等差数列{an}的前n项和为sn,若s6/s4=1/4,求s9/s32.设数列{an}的前n项和为sn,sn-2sn-1=2(n大于或等于2),a1=2(1)求证:数列{sn+2}是等比数列 (2)求sn (3)求an3.s6=9,s2=4,则s4=
由s6/s4=1/4,得:6(a1+a6)/(4(a1+a4))=1/4;所以:(a1+a6)/(a1+a4)=1/6;(2a1+5d)/(2a1+3d)=1/6;a1/d=-27/10;s9/s3=3(a1+a9)/(a1+a3)=3a5/a2=3(a1+4d)/(a1+d)=3*13/(-17)=-39/17;
2)因为:sn-2sn-1=2而sn*sn+2/(sn+1)^2=sn*sn+1*sn+2sn+1/(sn+1)^4=2*2/(sn+1)^4;在sn-2sn-1=2中,令n=2得:a0*(a0+2)=2,所以a0=-1+sqrt(3),或a0 =-1-sqrt(3);