4sn=an*2 2an-3

林永嘉,把分给我把,哈哈.Sn+S(n+1)=(5/3)a(n+1)=(5/3)[S(n+1)-Sn]4Sn=Sn+1Sn+1/Sn=4则,Sn成等比数列S1=a1Sn=4*4^(n-1)=4^n你的

1.Sn=-2an+3有S(n-1)=-2a(n-1)+3则an=Sn-S(n-1)=-2an+2a(n-1)=>an=a(n-1)*2/3所以,{an}为共比数列,q=2/32.Sn=-2an+3有

取倒数1/(Sn+1)=(4n+3)/Sn令bn=1/(Sn)得b1=1b(n+1)=bn*(4n+3)得b(n+1)/bn=4n+3(1)同理bn/(bn-1)=4(n-1)+3(2)...b2/b

当n=1时、有2s1+1=3a1,即有a1=1,因为2Sn+1=3an,所以2Sn+1+1=3an+1.后式减去前式,得2an+1=3an+1-3an.即有an+1=3an,为等比数列,且公比为3,所

s(n)+s(n+1)=(5/3)a(n+1),s(1)+s(2)=2a(1)+a(2)=(5/3)a(2),2a(1)=(2/3)a(2),a(2)=3a(1)=12.s(n+1)+s(n+2)=(

S1=A1=2A1-3故A1=3而An=Sn-S(n-1)=(2An-3n)-[2A(n-1)-3(n-1)]=2An-2A(n-1)-3故An=2A(n-1)+3故An+3=2[A(n-1)+3]即

n=1时,a1=1+3a1.即a1=-1/2.n>1时,an=Sn-Sn-1=1+3an-（1+3a(n-1））=3an-3a(n-1),即an=3/2a(n-1),即an=-1/2*(3/2)^(n

a(n+1)+an=4n-3,an+a(n-1)=4*(n-1)-3,故a(n+1)-a(n-1）=4,（n≥2)a1=2,a2=-1当n为奇数时,an=2+(n-1）/2*4=2n,a(n-1)=-

对3a(n+1)+an=4变形得：3[a(n+1)-1]=-(an-1)a(n+1)/an=-1/3an=8*(-1/3)^(n-1)+1Sn=8{1+(-1/3)+(-1/3)^2+……+(-1/3

An=6Sn/(An+3)6Sn=(An)^2+3Ann>=26S(n-1)=(A(n-1))^2+3A(n-1)6An=(An)^2+3An-(A(n-1))^2-3A(n-1)(An)^2-(A(

Sn+S(n+1)=5（a（n+1））/3因为S(n+1)=SN+A(N+1)所以Sn+SN+A(N+1)=5a（n+1）/32SN=2a（n+1）/3SN=a（n+1）/3S(N-1)=AN/3SN

你在步步高上看的题吧?前一阵子给人辅导做过这道题...这道题不是常规方法也用不了配凑系数出现新的等差等比数列这道题当时我们也研究了半天方法就是把a1,a2,a3,a4,...往后列,不要把a1=4带入

Sn=4An-3S(n-1)=4A(n-1)-3Sn-S(n-1)=An=4An-3-[4A(n-1)-3]=4an-3-4A(n-1)+3=4An-4A(n-1)3An=4A(n-1)An/A(n-

因为Sn+Sn-1=3an所以Sn-1+Sn-1+an=3an2Sn-1=2anSn-1=an因为Sn=an+1所以Sn-Sn-1=an+1-anan=an+1-an2an=an+1an+1/an=2

（1）当n=1时，a1＝s1＝14a21+12a1−34，解出a1=3，又4Sn=an2+2an-3①当n≥2时4sn-1=an-12+2an-1-3②①-②4an=an2-an-12+2（an-an

a(n+1)=4a(n)-3n+1,a(n+1)-(n+1)=4a(n)-4n=4[a(n)-n],{a(n)-n}是首项为a(1)-1=1,公比为4的等比数列a(n)-n=4^(n-1),a(n)=

(1)An=3(1+2^n)(2)由题知,Sn=2An+3n-12=6(2^n-1)+3nBn=(An-3)/(Sn-3n)(A(n+1)-6)=(3*2^n)/(6(2^n-1))(3(2^(n+1

数列{A(n)},A1=1,A(n+1)=3A(n)+4.求A(n)和S(n).1.A(n+1)=3A(n)+4--->A(n)=3A(n-1)+4==3[3A(n-2)+4]+4==(3^2)A(n

Sn=-2an+3Sn-1=-2an-1+3这两个式子相减sn-sn-1=-2an+2an-1即an=-2an+2an-1an=2/3an-1这是等比数列Sn=-2an+3代入n=1S1=-2a1+3

an+Sn=41a(n+1)+S(n+1)=2a(n+1)+Sn=422-1得2a(n+1)-an=0a(n+1)=1/2anan+Sn=4an≠0a(n+1)/an=1/2数列{an}是等比数列