Tính 3^3/2.5+3^3/5.8+3^3/8.11+..+3^3/302.305

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1. Đáp án:

    

   Giải thích các bước giải:

   ` 3^3/2.5+3^3/5.8+3^3/8.11+..+3^3/302.305`

   `=3^2.( 3/2.5+3/5.8+3/8.11+..+3/302.305)`

   `=9.(1/2-1/5+1/5-1/8+1/8-1/11+…+1/302-1/305)`

   `=9.(1/2-1/305)`

   `=9. 303/610`

   `=2727/610`

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2. `3^3/2.5 + 3^3/5.8 + 3^3/8.11 + … + 3^3/302.305`

   `= ( 3/2.5 + 3/5.8 + 3/8.11 + …. + 3/302.305 ) . 3²`

   `= ( 1/2 – 1/5 + 1/5 – 1/8 + 1/8 – 1/11 + … + 1/302 – 1/305) . 3²`

   `= ( 1/2 – 1/305 ) . 3²`

   `=   303/610 . 9`

   `= 2727/610`

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