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

Toán Lớp 6: CMR tổng S= 1 . 2 + 2 . 3 + 3 . 4 + 4 . 5 + –. + 99 . 100 + 100 . 101 please help me

Toán Lớp 6: CMR tổng S= 1 . 2 + 2 . 3 + 3 . 4 + 4 . 5 + ……… + 99 . 100 + 100 . 101
please help me

Comments ( 2 )

  1. Giải đáp+Lời giải và giải thích chi tiết:
    S  = 1 . 2 + 2 . 3 + 3 . 4 + … + 99 . 100 + 100 . 101
    3S = 3 . (1 . 2 + 2 . 3 + 3 . 4 + … + 99 . 100 + 100 . 101)
    3S = 1 . 2 . 3 + 2 . 3 . 3 + 3 . 4 . 3 + … + 99 . 100 . 3 + 100 . 101 . 3
    3S = 1 . 2 . 3 + 2 . 3 . (4 – 1) + 3 . 4 . (5 – 2) + … + 99 . 100 . (101 – 98) + 100 . 101 . (102 – 99)
    3S = 1 . 2 . 3 + 2 . 3 . 4 – 1 . 2 . 3 + 3 . 4 . 5 – 2 . 3 . 4 + … + 99 . 100 . 101 – 98 . 99 . 100 + 100 . 101 . 102 – 99 . 100 . 101
    3S = (1 . 2 . 3 – 1 . 2 . 3) + (2 . 3 . 4 – 2 . 3 . 4) + … + (99 . 100 . 101 – 99 . 100 . 101) + 100 . 101 . 102
    3S = 0 + 0 + … + 0 + 100 . 101 . 102
    3S = 100 . 101 . 102
    3S = 1030200
    S = 343400
    @Lee

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