Tính câu sau :3+9+27+………………..+6561.

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Tính câu sau :3+9+27+………………..+6561.

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Cherry 1 year 2020-10-21T23:57:00+00:00 2 Answers 65 views 0

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    0
    2020-10-21T23:58:05+00:00

    `A=3+9+27+………………..+6561`

    `A=3^1+3^2+3^3+…+3^8`

    `3A=3^2+3^3+3^4+…+3^8+3^ 9`

    `2A=3^9-3`

    `A=3^9-3:2`

    `19680:2=9840`

     

    0
    2020-10-21T23:58:17+00:00

    Giải thích các bước giải:

     $A=3+9+27+…+6561$

    $A=3^1+3^2+3^3+…+3^8$

    $3A=3^2+3^3+3^4+…+3^8+3^9$

    $2A=3^9-3$

    $A=\dfrac{3^9-3}{2}$

    $=\dfrac{19680}{2}=9840$

    Học tốt!!!

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