a: Ta có: \(3x\left(3x-1\right)-\left(3x+1\right)\left(3x-1\right)=0\)

\(\Leftrightarrow9x^2-3x-9x^2+1=0\)

\(\Leftrightarrow3x=1\)

hay \(x=\dfrac{1}{3}\)

b: Ta có: \(x^2-5x+25-5x=0\)

\(\Leftrightarrow\left(x-5\right)^2=0\)

\(\Leftrightarrow x-5=0\)

hay x=5

$ a/ 12x(x – 5) – 3x(4x - 10) = 120$

`<=>12x^2-60x-12x^2+30x=120`

`<=>-30x=120`

`<=>x=-4`

Vậy `x=-4`

$b/ 9x(x + 4) – 5x(3x + 2) = 112 - 2x(3x + 1)$

`<=>9x^2+36x-15x^2-10x=112-6x^2-2x`

`<=>-6x^2+26x=112-6x^2-2x`

`<=>28x=112`

`<=>x=4`

Vậy `x=4`

$c/ 3x(1 – x) - 5x(3x + 7) = 154 + 9x(5 – 2x)$

`<=>3x-3x^2-15x^2-35x=154+45x-18x^2`

`<=>-32x-18x^2=154+45x-18x^2`

`<=>77x=-154`

`<=>x=-2`

Vậy `x=-2`

a, \(-4x+5+2x-1=3\Leftrightarrow-2x=-1\Leftrightarrow x=\dfrac{1}{2}\)

b, \(-2x+2=2\Leftrightarrow x=0\)

c, \(-2x-6=-8\Leftrightarrow x=1\)

Ta có : x(x - 3) - 2x + 6 = 0

<=> x(x - 3) - (2x - 6) = 0

=> x(x - 3) - 2(x - 3) = 0

=> (x - 2)(x - 3) = 0

\(\Leftrightarrow\orbr{\begin{cases}x-2=0\\x-3=0\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}x=2\\x=3\end{cases}}\)

1 , <=>  25x^2 + 10x + 1 - ( 25x^2 - 9) = 30 

      <=> 25x^2 + 10x + 1 - 25x^2 + 9 = 30 

      <=> 10x + 10                 = 30 

     <=> 10 ( x + 1)                 = 30

       <=>  x + 1                      = 3 

        <=>  x                           = 2 

2, ( x + 3)(x^2 - 3x + 9 ) - x(x+2)(x-2) = 15 

<=> x^3 - 27 - x(x^2 - 4)                      = 15

<=> x^3 - 27 - x^3 + 4x                        = 15 

<=> 4x -27                                          = 15 

<=> 4x                                                = 15 + 27

<=> 4x                                                 =42

<=> x                                                     = 42/4 = 21/2 

******************

1,3x+2/5x+7 =3x-1/5x+1

<=> 1,3x+2/5x-3x+1/5x = 1-7

<=> (1,3+2/5-3+1/5)x = -6

<=> -11/10x=-6

<=> x= -6 : (-11/10)

<=> x= 60/11

2.x+1/2x+1 = 0,5x+2/x +3

<=> 2x+1/2x-0,5x-2/1x = 3-1

<=> x(2+1/2-0,5-2 ) =2

<=>0x =2

<=> x=0 

Hinh nhu minh thay ban Kunzy Nguyen giai hoi sai

1,3x o dau ra ???????????????

 Hình như bạn Kunzy Nguyễn ghi nhầm 3x thành 1,3x nhỉ ?!!!