早教吧 育儿知识 作业答案 考试题库 百科 知识分享

已知数列{an},{bn}的前n项和分别为An,Bn,且A100=8,B100=251.记Cn=an•Bn+bn•An-an•bn(n∈N*),则数列{Cn}的前100项的和为.

题目详情
已知数列{an},{bn}的前n项和分别为An,Bn,且A100=8,B100=251.记Cn=an•Bn+bn•An-an•bn(n∈N*),则数列{Cn}的前100项的和为______.
▼优质解答
答案和解析
Cn=an•Bn+bn•An-an•bn
=(An-An-1)×Bn+(Bn-Bn-1)×An-(An-An-1)×(Bn-Bn-1
=An×Bn-An-1×Bn+Bn×An-Bn-1×An-(An×Bn-An-1×Bn-An×Bn-1+An-1×Bn-1]
=An×Bn-An-1×Bn-1
∴Cn=An×Bn-An-1×Bn-1
Cn-1=An-1×Bn-1-An-2×Bn-2
…C2=A2×B2-a1×b1
C1=a1×b1
∴Cn=C1+C2+…+Cn-1+Cn
=a1×b1+(A2×B2-a1×b1)+…+(An-1×Bn-1-An-2×Bn-2)+(An×Bn-An-1×Bn-1)=An×Bn
∴C100=A100×B100=8×251=2008
C(100)=A(100)×B(100)=8×251=2008.
答案:2008.