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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 6: tính tổng S=6+6^2+6^3+6^4+…+6^99

Toán Lớp 6: tính tổng S=6+6^2+6^3+6^4+…+6^99

Comments ( 2 )

  1. \mathbb{S} = 6 + 6^2 + 6^3 + … + 6^99
    => 6\mathbb{S} = 6^2 + 6^3 + 6^4 + … + 6^100
    => 5\mathbb{S} = 6^100 – 6
    => \mathbb{S} = (6^100 – 6)/5

  2. S = 6 + 6^2 + 6^3 + 6^4 + … + 6^99
    6S = 6^2 + 6^3 + 6^4 + 6^5 + … + 6^100
    6S – S = (6^2 + 6^3 + 6^4 + 6^5 + … + 6^100) – (6 + 6^2 + 6^3 + 6^4 + … + 6^99)
    5S = 6^100 – 6
    S = (6^100 – 6)/5
     

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222-9+11+12:2*14+14 = ? ( )