a(n+1)=2an-a(n-1) 3bn-b(n-1)=n数列{an},a(n+1)=2an-a(n-1),a1=1/4,a2=3/4.数列{bn},3bn-b(n-1)=n,{bn}前n项和Sn1.求证数列{bn-an}是等比2.若当且仅当n=4时,Sn取得最小值,求b1取值范围

已知数列{an}满足a1=1,且an=1/3a(n-1)+(1/3)^n (n≥2,且n∈N+),则数列{an}的通项公式为A.an=3^n/(n+2) B.an=(n+2)/3^n C.an=n+2 D.an=(n+2)3^n 已知lim n→∞ (an^2/3n+1-n)=b,a+b=?[(an^2/3n+1)-n]=b 设bn=(n-1)/(an-2),(n大于等于2),an=n^a-n+2,且b(n+1)+b(n+2)+...b(2n+1) lim (n→∞) (n^2/(an+b)-n^3/(2n^2-1))=1/4 求a,b 是否存在常数a,b使等式1*n+2*(n-1)+3*(n-2)+...+n*1=an*(n+b)(n+2) lim(an^2/(3n+1)-n)=b a+b=? 已知数列an中,a1=2,an+1=3an+2^n(n+1为脚标),求an a(已知数列an中,a1=2,an+1=3an+2^n(n+1为脚标),求an a(n+1)=3an+2^na(n+1)+x*2^(n+1)=3(an+x*2^n)a(n+1)=3an+3x*2^n-x*2*2^na(n+1)=3an+x*2^nx=1a(n+1)+2^(n+1)=3(an+2^n)an+2^n=bn,b1=a1+2=4b(n+1)= 等差数列a-2d,a,a+2d,...的通项公式是( )A.an=a+(n-1)d B.an=a+(n-3)dC.an=a+2(n-2)d D.an=a+2nd 已知a1=2 a(n+1)=2an+2^n+3^n 求an 定义数列An=x^n+y^n+z^n,则A(n+3)-3A(n+2)+b*A(n+1)-c*An=0 这是为啥?b=xy+xz+yz,c=xyz 证明数列 an+a(n-1）b+a(n-2)b^2+...+ab^(n-1)+b^n=【a^(n+证明数列an+a(n-1）b+a(n-2)b^2+...+ab^(n-1)+b^n=【a^(n+1)-b^(n+1)]/(a-b) 已知：lim (n→∞) [(n^2+n)/(n+1)-an-b]=1 ,求a,b的值 数列{an},a1=3,an*a(n+1)=(1/2)^n,求an 已知数列｛an｝中,a(n+1)=an+2^n,a1=3,求an 已知数列{an}中,a1=1,a(n+1)>an,且[a(n+1)-an]^2-2[a(n+1)+an]+1=0,则an等于（ ）A、n B、n^2 C、n^3 D、√(n+3)-√n lim(n->无穷)[(3n^2+cn+1)/(an^2+bn)-4n]=5求常数a、b、c 已知an=3^(n-1) bn=3n-6 设cn=b(n+2)/a(n+2) ,求证c(n+1) 已知a1=3,a(n+1)=(3n-1)/(3n+2)an(n≥1),求an