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

Toán Lớp 7: 1/3 + 1/6 + 1/10 + 1/15 + -+1/x( 2x + 1)= 1/10

Toán Lớp 7: 1/3 + 1/6 + 1/10 + 1/15 + ….+1/x( 2x + 1)= 1/10

Comments ( 1 )

  1. Giải đáp + Lời giải và giải thích chi tiết:
    1/3+1/6+1/10+…+1/(x(2x+1))=1/10
    =>2(1/6+1/12+1/20+…+1/(2x(2x+1)))=1/10
    =>1/2.3+1/3.4+1/4.5+…+1/(2x(2x+1))=1/20
    =>1/2-1/3+1/3-1/4+1/4-1/5+…+1/(2x)-1/(2x+1)=1/20
    =>1/2-1/(2x+1)=1/20
    =>1/(2x+1)=9/20
    =>9(2x+1)=20
    =>2x+1=20/9
    =>2x=11/9
    =>x=11/18
     

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