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

Toán Lớp 6: chứng tỏ tổng S = 7+7^2+7^3+7^4+7^5+7^6 chia hết cho 57

Toán Lớp 6: chứng tỏ tổng S = 7+7^2+7^3+7^4+7^5+7^6 chia hết cho 57

Comments ( 1 )

  1. S = 7 + 7^2 + 7^3 + 7^4 + 7^5 + 7^6
    S = ( 7 + 7^2 + 7^3 ) + ( 7^4 + 7^5 + 7^6 )
    S = 7 . ( 1 + 7 + 7^2 ) + 7^4 . ( 1 + 7 + 7^2 )
    S = ( 1 + 7 + 7^2 ) . ( 7 + 7^4 )
    S = 57 . ( 7 + 7^4 ) vdots 57 ( Điều phải chứng minh )

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

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