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问题: 已知:f(n)=[1/(n+1)]+[1/(n+2)]+...+[1/(2n)]

已知:f(n)=[1/(n+1)]+[1/(n+2)]+...+[1/(2n)]
求: f(n+1)-f(n)

解答:

已知:f(n)=[1/(n+1)]+[1/(n+2)]+...+[1/(2n)]
求: f(n+1)-f(n)

已知:f(n)=[1/(n+1)]+[1/(n+2)]+...+[1/(2n)]
那么:
f(n+1)=[1/(n+1+1)]+[1/(n+1+2)]+...+[1/(2(n+1)]
=[1/(n+2)]+[1/(n+3)]+…+[1/(2n)]+[1/(2n+1)]+[1/(2n+2)]
所以:
f(n+1)-f(n)
=[1/(2n+1)]+[1/(2n+2)]-[1/(n+1)]
=[1/(2n+1)]-[1/(2n+2)]
=1/[(2n+1)(2n+2)]