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

Toán Lớp 7: tính nhanh B = -1/3 + 1/3 mũ 2 – 1/3 mũ 3 + – + 1/3 mũ 50 – 1/3 mũ 51

Toán Lớp 7: tính nhanh
B = -1/3 + 1/3 mũ 2 – 1/3 mũ 3 + …. + 1/3 mũ 50 – 1/3 mũ 51

Comments ( 2 )

  1. Giải đáp:B=(-1-1/3^51)/4.
     
    Lời giải và giải thích chi tiết:
    B=-1/3+1/3^2-1/3^3+….+1/3^50-1/3^51
    =>3B=-1+1/3-1/3^2+….+1/3^49-1/3^50
    =>3B+B=-1+1/3-1/3^2+….+1/3^49-1/3^50-1/3+1/3^2-1/3^3+….+1/3^50-1/3^51
    =>4B=-1-1/3^51
    =>B=(-1-1/3^51)/4.

  2. B = -1/3 + 1/3^2 – 1/3^3 + …. + 1/3^50 – 1/3^51
    3B = -1 + 1/3 – 1/3^2 + …. + 1/3^49 – 1/3^50
    3B+ B = (-1 + 1/3 – 1/3^2 + …. + 1/3^49 – 1/3^50) + ( -1/3 + 1/3^2 – 1/3^3 + …. + 1/3^50 – 1/3^51)
    4B= -1 – 1/3^51
    B = (-1 – 1/3^51)/4
    (Chúc bạn học tốt)
     

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