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

Toán Lớp 6: rút gọn biểu thức M= 1/1.2+1/2.7+-..+1/50.97

Toán Lớp 6: rút gọn biểu thức M= 1/1.2+1/2.7+……+1/50.97

Comments ( 2 )

  1. Giải đáp:
    text(M)=33/50
    Lời giải và giải thích chi tiết:
    text(M)=1/1.2+1/2.7+…+1/50.97
    =>text(M)/2=1/(1.2.2)+1/(2.2.7)+…+1/(2.50.97)
    =>text(M)/2=1/1.4+1/4.7+…+1/97.100
    =>(text(3M))/2=3/1.4+3/4.7+…+3/97.100
    =>(text(3M))/2=1-1/4+1/4-1/7+…+1/97-1/100
    =>(text(3M))/2=1-1/100
    =>(text(3M))/2=99/100
    =>text(M)/2=99/100:3
    =>text(M)/2=33/100
    =>text(M)=33/100*2
    =>text(M)=33/50
    Vậy text(M)=33/50.

  2. M = 1/{1 × 2} + 1/{2 × 7} + … + 1/{50 × 97}
    1/2 × M = 1/{1 × 4} + 1/{4 × 7} + … + 1/{97 × 100}
    1/2 × 3 × M = 3/{1 × 4} + 3/{4 × 7} + … + 3/{97 × 100}
    3/2 × M = 1/1 – 1/4 + 1/4 – 1/7 + … + 1/97 – 1/100
    3/2 × M = 1/1 – 1/100
    3/2 × M = 99/100
    => M = 99/100 : 3/2
    M = 198/300 = 33/50
    #dtkc
     

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