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

Toán Lớp 6: Cho `A=5+5^2+5^3+…+5^2020`. A có chia hết cho `65` không?

Toán Lớp 6: Cho A=5+5^2+5^3+…+5^2020. A có chia hết cho 65 không?

Comments ( 2 )

  1. A = 5 + 5² + 5³ +  ….. + 5^(2020)
    ⇒ A = (5 + 5² + 5³ + 5^4) + ……. + (5^(2009) + 5^(2010) + 5^(2011) + 5^(2012))
    ⇒ A = (5 + 25 + 125 + 625) + …… + 5^(2009) (5 + 25 + 125 + 625)
    ⇒ A = 780 + ….. + 5^(2009).780
    ⇒ A = ( 1 + …… + 5^(2009)).780 vdots 65
    Vậy A vdots 65

  2. A=5+5^2+5^3+…+5^2012
     ( 780 : 65 = 12 )

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

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