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1/(1×2)+1/(2×3)+1/(3×4)+...+1/(8×9)+1/(9×10)
=1-1/2+1/2-1/3+1/3-1/4+...+1/8-1/9+1/9-1/10
=1-1/10
=9/10
=1-1/2+1/2-1/3+1/3-1/4+...+1/8-1/9+1/9-1/10
=1-1/10
=9/10
1年前
4
你能帮帮他们吗
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