tìm x : (14x^3+12x^2-14x):2x=(x+2)(3x-4) (4x-5)(6x+1)-(8x+3)(3x-4)=15

        `(14x^3+12x^2-14x):2x=(x+2)(3x-4)`

`⇔(14x^3)/(2x) + (12x^2)/(2x) - (14x)/(2x)= 3x^2 -4x + 6x -8`

`⇔7x^2 + 6x - 7 = 3x^2 +2x-8`

`⇔7x^2 + 6x-7 - 3x^2 -2x+8=0`

`⇔(7x^2 -3x^2)+(6x-2x)+(8-7)=0`

`⇔4x^2 + 4x + 1=0`

`⇔(2x)^2 + 2.2x.1 +1^2=0`

`⇔(2x+1)^2=0`

`⇔2x+1=0`

`⇔2x=-1`

`⇔  x=-1/2`

Vậy, `x=-1/2`

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        `(4x-5)(6x+1)-(8x+3)(3x-4)=15`

`⇔24x^2 +4x - 30x - 5 - 24x^2 +32x -9x + 12-15=0`

`⇔(24x^2 -24x^2)+(4x+32x-30x-9x)-(5+15-12)=0`

`⇔-3x-8=0`

`⇔-3x=8`

`⇔   x=-8/3`

Vậy, `x=-8/3`

`#` $Mpro$