Tính S=1/3+1/9+1/18+1/39+1/45+1/63+…+1/14850

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1. Đáp án:

    

   Giải thích các bước giải:

   `S=1/3+1/9+1/18+1/39+1/45+1/63+…+1/14850`

   `S=1/1.3+1/3.3+1/3.6+1/3.15+1/3.21+…+1/3.4950`

   `S/3=1+1/3+1/6+1/15+1/21+…+1/4950`

   `S/6=1/2+1/6+1/12+1/30+1/42+…+1/9900`

   `S/6=(1/1.2+1/2.3+1/3.4+1/4.5+1/5.6+1/6.7+…+1/99.100)-1/4.5`

   `S/6=(1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+…+1/99-1/100)-1/4-1/5`

   `S/6=(1-1/100)-1/4-1/5` `S/6=99/100-(1/4+1/5)`

   `S/6=99/100-9/20`

   `S/6=27/50` 

   `S=27/50*6`

   `S=81/25`

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