问题
解答题
设数列{an}是公差为d,且首项为a0=d的等差数列,求和:Sn+1=a0
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答案
由数列{an}是公差为d,且首项为a0=d的等差数列
得:an=a0+(n+1-1)d=(n+1)d;
∴Sn+1=a0
+a1C 0n
+…+anC 1n
,C nn
又Sn+1=an
+an-1C nn
+…+a0C n-1n C 0n
=an
+an-1C 0n
+…+a0C 1n
,C nn
∴2Sn+1=(a0+an)C
+(a1+an-1) 0n
+…+(an+a0)C 1n C nn
=(a0+an)(
+C 0n
+…+C 1n
)=(a0+an)2nC nn
∴Sn+1=(a0+an)•2n-1.