rút gọn ( x- 3) (x^2 +3x +9)-(x^2 +3)(x- 9) tìm x (2x-3 ) (3+2x) -x (x-1 ) =3(x-1)^2

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1. Đáp án:

   `( x- 3) (x^2 +3x +9)-(x^2 +3)(x- 9)`

   `=x^3-27-[x^3-9x^2+3x-27)`

   `=x^3-27-x^3+9x^2-3x+27`

   `=9x^2-3x`

   `=3x(3x-1)`

   tìm `x`

   `(2x-3 )(3+2x)-x(x-1 )=3(x-1)^2`

   `<=>(2x-3 )(3+2x)-x(x-1 )-3(x-1)^2=0`

   `<=>4x^2-9-x^2+x-3(x^2-2x+1)=0`

   `<=>4x^2-9-x^2+x-3x^2+6x-3=0`

   `<=>-12+7x=0`

   `<=>7x=0+12`

   `<=>7x=12`

   `<=>x=12/7`

    

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2. Đáp án:

   `(x-3)(x^2+3x+9)-(x^2+3)(x-9)`

   `=x^3-27-(x^3-9x^2+3x-27)`

   `=x^2-27-x^3+9x^2-3x+27`

   `=9x^2-3x`

   `———–`

   `(2x-3)(3+2x)-x(x-1)=3(x-1)^2`

   `=> 4x^2-9-x^2+x=3(x^2-2x+1)`

   `=> 3x^2+x-9=3x^2-6x+3`

   `=> 3^x-3x^2+x+6x=3+9`

   `=> 7x=12`

   `=> x=12/7`

    

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