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

Toán Lớp 7: Tính A’ = 1 + 5 + 5^2 + 5^4 + 5^6 + … + 5^1000

Toán Lớp 7: Tính
A’ = 1 + 5 + 5^2 + 5^4 + 5^6 + … + 5^1000

Comments ( 2 )

  1. #laviken#
    A’=1+5+5^2+5^4+5^6+…+5^1000
    =>5A’=5(1+5+5^2+5^4+5^6+…+5^1000)
    =>5A’=5+5^2+5^4+5^6+…+5^1001
    =>5A’-A’=(5+5^2+5^4+5^6+…+5^1001)-(1+5+5^2+5^4+5^6+…+5^1000)
    =>4A’=5^1001-1
    =>A’=(5^1001-1)/4
     

  2. A’ = 1 + 5 + 5^2 + 5^4 + 5^6 + … + 5^(1000)
    ⇔5A’=  5 + 5^2 + 5^4 + 5^6 + … + 5^(1001)
    ⇔4A’=5^(1001)-1
    ⇔A’=(5^(1001)-1)/4

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