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

Toán Lớp 7: cho A=2+$2^{2}$+$2^{3}$+…+$2^{60}$ chứng minh A⋮3,A⋮7,A⋮5 đây

Toán Lớp 7: cho A=2+$2^{2}$+$2^{3}$+…+$2^{60}$
chứng minh A⋮3,A⋮7,A⋮5
đây

Comments ( 2 )

  1. A = 2 + 22 + 23 + 24 + … + 260
    A = (2 + 22) + (23 + 24) + … + ( 259 + 260)
    A = 1.(2 + 22) + 22(2 + 22) + …+ 258.(2 + 22)
    A = 1 . 6 + 22 . 6 + … + 258 . 6
    A = 6 . (1 + 2+… + 258) 3
     
     
     
     
    ⇒ A⋮ 7
    ⇔ 
    ⇔ 
    ⇔ 
    ⇔ 
    ⇒ A⋮ 15
    ⇒ A⋮5

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