问题标题:
猜想Sn=1/1*2+1/2*3,...,1/n*(n+1)的表达式,并用数学归纳法证明
问题描述:
猜想Sn=1/1*2+1/2*3,...,1/n*(n+1)的表达式,并用数学归纳法证明
郭新宇回答:
Sn=1/1*2+1/2*3,...,1/n*(n+1)
=(1-1/2)+(1/2-1/3)+.+[1/n-1/(n+1)]
=1-1/(n+1)
=n/(n+1)
用数学归纳法证:
当k=1时:S1=1/1*2=1/2k/(k+1)=1/2所以Sk=k/(k+1)
假设当k=n时成立,即:Sn=n/(n+1)
那么当k=n+1时,证明S(n+1)=(n+1)/(n+2)即可
S(n+1)=1/1*2+1/2*3,...,1/n*(n+1)+1/(n+1)(n+2)
=n/(n+1)+1/(n+1)(n+2)
=n(n+2)/(n+1)(n+2)+1/(n+1)(n+2)
=(n^2+2n+1)/(n+1)(n+2)
=(n+1)^2/(n+1)(n+2)
=(n+1)/(n+2)
所以综上:Sn=n/(n+1)
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