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

Toán Lớp 8: TÌM X BIẾT a) x ( x – 6 ) – x^2 = 18 b) 25x^2 – 64 = 0

Toán Lớp 8: TÌM X BIẾT
a) x ( x – 6 ) – x^2 = 18
b) 25x^2 – 64 = 0

Comments ( 2 )

  1. a)x(x-6)-x^2=18
    <=>x^2-6x-x^2=18
    <=> -6x=18
    <=>x=-3
    Vậy x=-3
    b)25x^2-64=0
    <=>(5x)^2-8^2=0
    <=>(5x+8)(5x-8)=0
    <=>[(5x+8=0),(5x-8=0):}
    <=>[(5x=-8),(5x=8):}
    <=>$\left[\begin{matrix} x=-\dfrac{8}{5}\\ x=\dfrac{8}{5}\end{matrix}\right.$
    Vậy x=-8/5 hoặc x=8/5

  2. Giải đáp+Lời giải và giải thích chi tiết:
    a)  x(x-6)-x^2=18
    ⇔x.x+x.(-6)-x^2=18
    ⇔x^2-6x-x^2=18
    ⇔(x^2-x^2)-6x=18
    ⇔-6x=18
    ⇔x=-3
       Vậy x=-3
    b)  25x^2-64=0
    ⇔(5x)^2-8^2=0
    ⇔(5x-8)(5x+8)=0
    $⇔\left[\begin{matrix} 5x-8=0\\ 5x+8=0\end{matrix}\right.$
    $⇔\left[\begin{matrix} 5x=8\\ 5x=-8\end{matrix}\right.$
    $⇔\left[\begin{matrix} x=\dfrac{8}{5}\\ x=-\dfrac{8}{5}\end{matrix}\right.$
        Vậy x=8/5 hoặc x=- 8/5 
    ->Áp dụng HĐT: A^2-B^2=(A-B)(A+B)
    $\text{#LinhSad}$

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

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