已知等差数列{an}的公差d〉0,且a2、a5满足a2+a5=12,a2a5=27.数列{bn}的前n项和为Sn,且Sn
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已知等差数列{an}的公差d〉0,且a2、a5满足a2+a5=12,a2a5=27.数列{bn}的前n项和为Sn,且Sn=(-1/2bn)(n属于正整数)
1.数列{an}{bn}的通向公式.
2.求Tn=b2+b4+b6+...+b2n.
1.数列{an}{bn}的通向公式.
2.求Tn=b2+b4+b6+...+b2n.
由a2+a5=12,a2a5=27可知
a2=3、a5=9或a2=9、a5=3(舍去)
d=(a5-a2)/3=2,a1=a2-d=1
an=a1+(n-1)d=2n-1
Sn=(-1/2bn)=-1/2(Sn-Sn-1)
Sn/Sn-1=1/3
S1=b1=-1/2b1,b1=0
Sn=0,即Bn=0
Tn=0
我怀疑题目有问题
a2=3、a5=9或a2=9、a5=3(舍去)
d=(a5-a2)/3=2,a1=a2-d=1
an=a1+(n-1)d=2n-1
Sn=(-1/2bn)=-1/2(Sn-Sn-1)
Sn/Sn-1=1/3
S1=b1=-1/2b1,b1=0
Sn=0,即Bn=0
Tn=0
我怀疑题目有问题
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