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

Toán Lớp 6: A=11/2×4 + 11/4×6 + 11/6×8+11/8×10- + 11/98×100

Toán Lớp 6: A=11/2×4 + 11/4×6 + 11/6×8+11/8×10….
+ 11/98×100

Comments ( 2 )

  1. Giải đáp:
     
    Lời giải và giải thích chi tiết:
    A=11/(2xx4)+11/(4xx6)+11/(6xx8)+…+11/(98xx100)
    =>A/11=1/(2xx4)+1/(4xx6)+1/(6xx8)+…+1/(98xx100)
    =>(2A)/11=2/(2xx4)+2/(4xx6)+2/(6xx8)+…+2/(98xx100)
    =>(2A)/11=1/2-1/4+1/4-1/6+1/6-1/8+…+1/98-1/100
    =>(2A)/11=1/2-1/100
    =>(2A)/11=49/100
    =>2A=49/100xx11
    =>2A=539/100
    =>$A=\dfrac{539}{100}:2$
    =>A=539/200
    Vậy A=539/200.

  2. A = 11/( 2 xx 4)+ 11/( 4 xx 6) + 11/( 6 xx 8) + 11/( 8 xx 10) + … + 11/( 98 xx 100)
    = 11/2 xx (2/( 2 xx 4)+ 2/( 4 xx 6) + 2/( 6 xx 8) + 2/( 8 xx 10) + … + 2/( 98 xx 100))
    = 11/2 xx ( 1/2 – 1/4 + 1/4 – 1/6 + 1/6 – 1/8 + 1/8 – 1/10 + …. + 1/98 – 1/100)
    = 11/2 xx ( 1/2 – 1/100)
    = 11/2 xx  49/100
    = 539/200
    Vậy A = 539/200

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