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

Toán Lớp 5: 2/3 x 5 + 2/5 x7 + 2/7 x9 +2/9 x 11+…+2/13 x 15

Toán Lớp 5: 2/3 x 5 + 2/5 x7 + 2/7 x9 +2/9 x 11+…+2/13 x 15

Comments ( 2 )

  1. Giải đáp:
     
    Lời giải và giải thích chi tiết:
     2/3×5 + 2/5 x 7 + 2/7 x 9 + 2/9 x 11 + … + 2 /13 x 15 
    = (1/3 – 1/5 + 1/5 – 1/7 + 1/7 – 1/9 + 1/9 – 1/11 + … + 1/13 -1/15) x 2
    = (1/3 – 1/15 ) x 2
    = 4 / 15 x 2 
    = 8/15

  2. 2/{3 × 5} + 2/{5 × 7} + … + 1/{13 × 15}
    = 2×(1/{3× 5} + 1/{5 × 7} + … + 1/{13 × 15})
    = 2 × ( 1/3 – 1/5 + 1/5 – 1/7 + … + 1/13 – 1/15 )
    = 2 × ( 1/3 – 1/15 )
    = 2 × 4/15
    = 8/15
    #dtkc

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

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