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问题: 求解:1+1/1+2+1/1+2+3+/1+2+3+4+1/1+2+3+4+......+99

解答:

1+2+3+...+n = n(n+1)/2

1/(1+2+3+...+n) = 2/[n(n+1)] = 2[ 1/n - 1/(n+1) ]

1+1/(1+2)+1/(1+2+3)+/(1+2+3+4)+...+1/(1+2+3+4+...+99)
=1+[1-1/2]+[1/2-1/3]+[1/3-1/4]+...+[1/99-1/100]
=1+1-1/100
=1.99