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

Toán Lớp 7: a. 1/1.3 + 1/3.5+1/5.7 +-+1/19.21 b. 1/99-1/99.97-1/97.95-1/95.93=1/5.3-1/3.1

Tháng Hai 7, 2023 Toán học 2 Comments 0 views

Toán Lớp 7: a. 1/1.3 + 1/3.5+1/5.7 +….+1/19.21
b. 1/99-1/99.97-1/97.95-1/95.93-….-1/5.3-1/3.1

Comments ( 2 )

  1. buianhtuan
    buianhtuan
    7 Tháng Hai, 2023 at 7:18 chiều
    Reply
    1/(1.3) + 1/(3.5)+1/(5.7) +….+1/(19.21)
    = 1/2 . (2/(1.3) + 2/(3.5)+2/(5.7) +….+2/(19.21))
    = 1/2 . (1-1/3+1/3-1/5+1/5-1/7+….+1/19 – 1/21)
    = 1/2 . (1 – 1/21)
    = 1/2 . 20/21
    = 10/21
    1/99-1/(99.97)-1/(97.95)-1/(95.93)-….-1/(5.3)-1/(3.1)
    = 1/99 – (1/(99.97)+1/(97.95)+1/(95.93)+….+1/(5.3)+1/(3.1))
    = 1/99 – (1/(1.3)+1/(3.5)+1/(5.7)+….+1/(95.97)+1/(97.99))
    = 1/99 – (1/(1.3)+1/(3.5)+1/(5.7)+….+1/(95.97)+1/(97.99))
    = 1/99 – (1/2 . (1/(1.3)+1/(3.5)+1/(5.7)+….+1/(95.97)+1/(97.99)))
    = 1/99 – (1/2 . (1-1/3+1/3-1/5+1/5-1/7+….+1/95-1/97+1/97-1/99))
    = 1/99 – (1/2 . (1-1/99))
    = 1/99 – (1/2 . 98/99)
    = 1/99 – 49/99
    = -16/33
    (Chúc bạn học tốt)

  2. tuminh25
    tuminh25
    7 Tháng Hai, 2023 at 7:18 chiều
    Reply
    a)
    1/1.3+1/3.5+1/5.7+1/19.21
    =1/2(2/1.3+2/3.5+2/5.7+…+2/19.21)
    =1/2(1-1/3+1/3-1/5+1/5-1/7+…+1/19-1/21)
    =1/2(1-1/21)
    =1/2. 20/21
    =10/21
    b)
    1/99-1/99.97-1/97.95-1/95.93-…-1/3.1
    =1/99-(1/1.3+1/3.5+1/5.7+…+1/97.99)
    =1/99-1/2(2/1.3+2/3.5+2/5.7+…+2/97.99)
    =1/99-1/2(1-1/3+1/3-1/5+1/5-1/7+…+1/97-1/99)
    =1/99-1/2(1-1/99)
    =1/99-1/2 . 98/99  
    =1/99-49/99
    =-16/33
     

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

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