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

Toán Lớp 6: Cho `A = 7/4 + 17/9 + 31/16 + … + 4999/2500`. Chứng minh `A>97`.

Toán Lớp 6: Cho A = 7/4 + 17/9 + 31/16 + … + 4999/2500. Chứng minh A>97.

Comments ( 2 )

  1. Giải đáp + Lời giải và giải thích chi tiết:
    A=7/4+17/9+31/16+…+4999/2500
    =>A=(1+3/4)+(1+8/9)+(1+15/16)+…+(1+2499/2500)
    =>A=(1+1+1+…+1)+(3/4+8/9+15/16+…+2499/2500)
    =>A=49+[(1-1/4)+(1-1/9)+(1-1/16)+…+(1-1/2500)]
    =>A=49+[(1+1+1+…+1)-(1/4+1/9+1/16+…+1/2500)]
    =>A=49+49-(1/4+1/9+1/16+…+1/2500)
    =>A=98-(1/4+1/9+1/16+…+1/2500)
    =>A=97+[1-(1/4+1/9+1/16+…+1/2500)]>97
    Vậy A>97
     

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