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10

发布时间:2020-07-31 18:04:08

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________.

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2008

解析分析:由题意可知Cn=An×Bn-An-1×Bn-1,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,由此可以求出数列{Cn}的前100项的和.

解答: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×b1C1=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=2008C(100)=A(100)×B(100)=8×251=2008.
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