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

Toán Lớp 8: tìm x biết 4x^2 – 9 – x(3 – 2x) = 0

Toán Lớp 8: tìm x biết 4x^2 – 9 – x(3 – 2x) = 0

Comments ( 2 )

  1. 4x^2-9-x(3-2x)=0
    <=>(4x^2-9)+x(2x-3)=0
    <=>(2x+3)(2x-3)+x(2x-3)=0
    <=>(2x-3)(2x+3+x)=0
    <=>(2x-3)(3x+3)=0
    <=>[(2x-3=0),(3x+3=0):}
    <=>[(2x=3),(3x=-3):}
    <=>$\left[\begin{matrix} x=\dfrac{3}{2}\\ x=-1\end{matrix}\right.$
    Vậy x=3/2 hoặc x=-1

  2. 4x^2-9-x(3-2x)=0
    ⇔(2x)^2-3^2+x(2x-3)=0
    ⇔(2x-3)(2x+3)+x(2x-3)=0
    ⇔(2x-3)(2x+3+x)=0
    ⇔(2x-3)(3x+3)=0
    ⇔3(2x-3)(x+1)=0
    ⇔(2x-3)(x+1)=0
    ⇔2x-3=0⇔2x=3⇔x=3/2
    x+1=0⇔x=-1
    Vậy x={3/2,-1}
    $_Ativity_$

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