an是等差数列,bn是各项都为正数的等比数列,且a1+b1=1,a3+b5=19,a5+b3=9.

来源：学生作业帮编辑：作业帮分类：数学作业时间：2024/05/27 18:35:12

an是等差数列,bn是各项都为正数的等比数列,且a1+b1=1,a3+b5=19,a5+b3=9.
（1）求｛an｝,｛bn｝的通项公式
（2）求数列｛an*bn｝的前n项和Sn.
是a1+b1=1。

a1=b1=1
a3+b5=1+2d+q^4=19
2d+q^4=18
2d=18-q^4
d=9-q^4/2
a5+b3=1+4d+q^2=9
4d+q^2=8
4d=8-q^2
d=2-q^2/4
9-q^4/2=2-q^2/4
7-q^4/2+q^2/4=0
2q^4-q^2-28=0
(q^2-4)(2q^2+7)=0(2q^2+7>0)
q^2=4{bn}是各项都为正数
q>0
q=2
d=2-q^2/4=2-2^2/4=1
an=a1+(n-1)d
=1+(n-1)
=n
bn=b1q^n-1
=2^n-1
a1=1
a2=2
a3=3
...
an=n
b1=1
b2=2
b3=4
...
bn=2^n-1
S=1*2^0+2*2^1+3*^2+4*2^3+.+n*2^n-1
2S=1*2^1+2*2^2+3*2^3+.+n*2^n
2S-s=-2^0-2^1-2^2-2^3-.2^n-1+n*2^n
=-(2^0+2^1+2^2+2^3+.+2^n-1)+n*2^n
=-[(1-2^n)/(1-2)]+n*2^n
=1-2^n+n*2^n
=1+(n-1)*2^n

an是等差数列,bn是各项都为正数的等比数列,且a1+b1=1,a3+b5=19,a5+b3=9. 设{an}是等差数列,{bn}是各项都为正数的等比数列且a1=b1=1,a3+b5=21,a5+b3=13.求{an}, 设{an}是等差数列,{bn}是各项都为正数的等比数列且a1=b1=1,a3+b5=21,a5+b3=13.求[an}, 设{an}是等差数列,{bn}是各项都为正数的等比数列,且a1=b1=1,a3+b5=21,a5+b3=13,求{an} an是等差数列,bn是各项都为正数的等比数列,且a1+b1=2,a3+b5=19,a5+b3=9 设{an}是等差数列,{bn}是各项都为正数的等比数列,且a1=b1=1,a3+b5=21,a5+b3=13 (1)求{ 设{an}是等差数列,{bn}是各项都为正数的等比数列且a1=b1=1,a3+b5=21,a5+b3=13. 设an是等差数列,bn是各项都为正数的等比数列,且a1=b1=1,a5+b3=13 a3+b5=21 设{an}是等差数列,{bn}是各项都为正数的等比数列,且a1=b1=1,a3+b5=21,a5+b3=13 AN是等差数列,BN是各项都为正数的等比数列,且A1=B1=1,A3+B5=21,A5+B3=13 设{an}是等差数列,{bn}是各项都为正数的等比数列且a1=b1=1,a3+b5=21,a5+b3=13 {an}是等差数列,{bn}是各项都为正数的等比数列,且a1=b1=1,a3+b5=21,a5+b3=13