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问题: 计算

(1/x(x+1))+(1/(x+1)(x+2))+(1/(x+2)(x+3))+(1/(x+3)(x+4))

解答:

1/x(x+1)+1/(x+1)(x+2)+1/(x+2)(x+3)+1/(x+3)(x+4)
=1/x-1/(x+1)+1/(x+1)-1/(x+2)+1/(x+2)-1/(x+3)+1/(x+3)-1/(x+4)
=1/x-1/(x+4)
=4/x(x+4)