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

Toán Lớp 7: 132 + 1/3 mũ 2 + 1/3 mũ 3 + chấm chấm chấm + 1/2 mũ 2020 giúp mik vs mn

Tháng Hai 23, 2023 Toán học 2 Comments 0 views

Toán Lớp 7: 132 + 1/3 mũ 2 + 1/3 mũ 3 + chấm chấm chấm + 1/2 mũ 2020
giúp mik vs mn

Comments ( 2 )

  1. maitrucloan
    maitrucloan
    23 Tháng Hai, 2023 at 1:53 sáng
    Reply
    Đặt A=1/3+1/3^2+1/3^3+…+1/3^2020
    ⇒3A=1+1/3+1/3^2+…+1/3^2019
    ⇒3A-A=(1+1/3+1/3^2+…+1/2^2019)-(1/3+1/3^2+1/3^3+…+1/3^2020)
    ⇒2A=1-1/3^2020
    ⇒2A={3^2020-1}/3^2020
    ⇒A={3^2020-1}/3^2021

  2. mocmien87
    mocmien87
    23 Tháng Hai, 2023 at 1:52 sáng
    Reply
    Giải đáp:
    $\\$
    Đề 1/3 + 1/3^2 + 1/3^3 + … + 1/3^{2020}
    Đặt A = 1/3 + 1/3^2 + 1/3^3 + … + 1/3^{2020}
    ↔ 3A = 3 (1/3 + 1/3^2 + 1/3^3 + … + 1/3^{2020})
    ↔ 3A = 1 + 1/3 + 1/3^2 + … + 1/3^{2019}
    ↔ 3A – A = (1 + 1/3 + 1/3^2 + … + 1/3^{2019})- (1/3 + 1/3^2 + 1/3^3 + … + 1/3^{2020})
    ↔ (3-1) A= 1 – 1/3^{2020}
    ↔ 2A =1 – 1/3^{2020}
    ↔ A = (1 – 1/3^{2020})/2
    Vậy A = (1 – 1/3^{2020})/2
    $\\$
    Đề 1/2 + 1/2^2 + 1/2^3 + … + 1/2^{2020}
    Đặt A = 1/2 + 1/2^2 + 1/2^3 + … + 1/2^{2020}
    ↔ 2A = 2 (1/2 + 1/2^2 + 1/2^3 + … + 1/2^{2020})
    ↔ 2A = 1 + 1/2 + 1/2^2 + … + 1/2^{2019}
    ↔ 2A – A = (1 + 1/2 + 1/2^2 + … + 1/2^{2019}) – (1/2 + 1/2^2 + 1/2^3 + … + 1/2^{2020})
    ↔ (2-1)A = 1 – 1/2^{2020}
    ↔ A = 1 – 1/2^{2020}
    Vậy A = 1- 1/2^{2020}
     

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

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