a1 3an
若数列{an}中,a1=3,且an+1=3an,则其前n项和Sn=
an+1=3an 3an-an=1 公差d=1/2 Sn=a1+a2+a3.an=n(a1+an)/2=n(a1+(a1+(n-1)d))=5*n*n/2
已知数列an,a1=3an+1=4an - 3设bn=log2(an - 1),求数列bn的前...
a(n+1)=4an－3 a(n+1) -1= 4(an-1)an-1 = 4^(n-1) .( a1-1)= 2.4^(n-1)an = 1+ 2.4^(n-1)= ...
已知a1=3,an=3an+1,求an
已知数列{an}中,a1=1,an+1=3an/(an+3)(N∈N*),求通项an, 已知数列{an}满足a1=1,a2=3,an+2=3an+1-2an求an 已知数列{an}中...
已知数列an中a1=3an分之an+1=3n+2分之3n - 1求通项公式an - 百...
a1=3 a(n+1)/an=(3n-1)/(3n+2)则a(n+1)(3n+2)=an(3n-1)因此{an(3n-1)}是公差为1的等差数列，首项为2a1=6...
a1=1,3an - 2sn=2n - 1,求证an+1为等比数列
an = a1 * q^(n-1)an+1 = a1 * q^n 通过已知的递推式，得到：3an-2 = 2n-1 那么：3a1 * q^(n-1) - 2 = ...
设数列{an}中,a1=3,并且3an+1=2an,则a4等于多少
所以an 是以2/3为公比的等比数列 an=a1q^(n-1)=3*(2/3)^(n-1)a4=3*(2/3)^(4-1)=3*8/27 =8/9 ...
在数列{an}中,满足a1=1,an+1=3an,则an= - - - .
解答:解:∵an+1=3an,∴an+1an=3,∴数列是一个等比数列,∴an=3n-1故答案为:3n-1
数列前N项和在数列{an}中,a1=1,an+1=3an+3^n,求数列{...
在数列{an}中,a1=1,a(n+1)=3an+3^n,求数列{an}的前n项和.用嵌套递推法求an:∵a(n+1)=3an+3^n∴an=3a(n-1)+3...
已知数列{an}中,a1=1,an=3an - 1+4,(n∈N*且n≥2),则...
解答:解:∵an=3an-1+4,∴an+2=3(an-1+2),∵a1+2=3,∴{an+2}是公比为3,首项是4的等比数列,即an+2=3×3n-1,an=...
已知数列{an}满足an+1=3an+3n,且a1=1,求an.
由an+1=3an+3n,得an+1+x(n+1)+y=3(an+xn+y),即an+1=3an+3xn+3y-x(n+1)-y=3an+2xn+2y-x.类比an+1=3an+3n...