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

Toán Lớp 6: So sánh C=3+3^2+3^3+…+3^100 và D= 3^101-3 phần 2

Toán Lớp 6: So sánh C=3+3^2+3^3+…+3^100 và D= 3^101-3 phần 2

Comments ( 2 )

  1. C=3+3^2+. . .+3^100
    3C=3^2+3^3+. . .+3^101
    3C-C=(3^2+3^3+. . .+3^101)-(3+3^2+. . .+3^100)
    2C=3^101-3
    C=$\dfrac{3^{101}-3}{2}$ 
    ⇒ C = D

  2. C=3+3^2+3^3+…+3^100
    3C=3^2+3^3+3^4+…+3^101
    3C-C=(3^2+3^3+3^4+…+3^101)-(3+3^2+3^3+…+3^100)
    2C=3^101 -3
    C=(3^101 -3)/2
    Mà (3^101 -3)/2=(3^101 -3)/2
    =>C=D

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