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

Toán Lớp 6: D=1/5.7+1/7.9+1/9.11+…+1/93.95

Toán Lớp 6: D=1/5.7+1/7.9+1/9.11+…+1/93.95

Comments ( 2 )

  1. Giải đáp:
     D=9/95
    Lời giải và giải thích chi tiết:
     D=1/5.7 +1/7.9 +1/9.11 +…+1/93.95
    => 2.D=2/5.7 +2/7.9 +2/9.11 +…+2/93.95
    => 2.D={7-5}/5.7 +{9-7}/7.9 +{11-9}/9.11 +…+ {95-93}/93.95
    => 2.D=1/5-1/7+1/7-1/9+1/9-1/11+…+1/93-1/95
    => 2.D=1/5-1/95
    => 2.D=19/95 -1/95
    => 2.D=18/95
    => D=18/95 :2
    =>D=18/95 . 1/2
    =>D=9/95

  2. D = 1/5.7 + 1/7.9 + 1/9.11 + … + 1/93.95
    2D = 2 . (1/5.7 + 1/7.9 + 1/9.11 + … + 1/93.95)
    2D = 2/5.7 + 2/7.9 + 2/9.11 + … + 2/93.95
    2D = 1/5 – 1/7 + 1/7 – 1/9 + 1/9 – 1/11 + … + 1/93 – 1/95
    2D = 1/5 – 1/95
    2D = 19/95 – 1/95
    2D = 18/95
    D = 18/95 : 2
    D = 18/190
    D = 9/95

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