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

Toán Lớp 8: 6x/x^3-9x + 5x/x^2-3x + x/x^2+3x

Toán Lớp 8: 6x/x^3-9x + 5x/x^2-3x + x/x^2+3x

Comments ( 2 )

  1. Giải đáp:
    6/(x-3) 
    Lời giải và giải thích chi tiết:
    (6x)/(x^3 -9x)+(5x)/(x^2 -3x)+ x/(x^2 +3x)
    =(6x)/(x(x^2-9))+(5x)/(x(x-3))+ x/(x(x+3))
    =6/(x^2-9)+ 5/(x-3) + 1/(x+3)
    =6/((x-3)(x+3))+5/(x-3) +1/(x+3)
    =(6+5(x+3)+x-3)/((x-3)(x+3))
    =(6+5x+15+x-3)/((x-3)(x+3))
    =(6x+18)/((x-3)(x+3))
    =(6(x+3))/((x-3)(x+3))
    =6/(x-3)

  2. Ta có: 
    x^3 -9x = x(x^2 -9)=x(x-3)(x+3)
    x^2 -3x=x(x-3)
    x^2 +3x=x(x+3)
    Quy đồng:
    (6x)/(x^3-9x) = (6x)/(x(x-3)(x+3)) 
    (5x)/(x^2-3x) = (5x(x+3))/(x(x-3)(x+3)) = (5x^2 +15x)/(x(x-3)(x+3))
    x/(x^2 +3x) = (x(x-3))/(x(x-3)(x+3)) = (x^2 -3x)/(x(x-3)(x+3))
    Vậy: (6x)/(x^3-9x) + (5x)/(x^2-3x) + x/(x^2 +3x)
    = (6x)/(x(x-3)(x+3)) + (5x^2 +15x)/(x(x-3)(x+3)) + (x^2 -3x)/(x(x-3)(x+3))
    = (6x+5x^2 +15x+x^2 -3x)/(x(x-3)(x+3))
    = (6x^2 +18x)/(x(x-3)(x+3))
    = (6x(x+3))/(x(x-3)(x+3))
    = (6)/(x-3)

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