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

Toán Lớp 6: Rút gọn biểu thức A = 1 + 3 + 3^2 + 3^3 + … + 3^99 + 3^100

Toán Lớp 6: Rút gọn biểu thức
A = 1 + 3 + 3^2 + 3^3 + … + 3^99 + 3^100

Comments ( 2 )

  1. A=1+3+3^2+3^3+…+3^100
    3A=3+3^2+3^3+…+3^100+3^101
    3A-A=3+3^2+3^3+…+3^100+3^101
              -1+3+3^2+3^3+…+3^100
             =3^101-1
    ⇒2A=3^101-1
    ⇒A=(3^101-1)/2

  2. A = 1 + 3 + $3^{2}$ $3^{3}$ +…+ $3^{99}$ + $3^{100}$
    3A = 3 + $3^{2}$ $3^{3}$ +…+ $3^{99}$ + $3^{100}$ + $3^{101}$
    3A – A = (3 + $3^{2}$ $3^{3}$ +…+ $3^{99}$ + $3^{100}$ + $3^{101}$) – (1 + 3 + $3^{2}$ $3^{3}$ +…+ $3^{99}$ + $3^{100}$).
    2A = $3^{101}$ – 1
    A = $\dfrac{3^{101} – 1}{2}$
    Xin hay nhất ạ!
     
     

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