\(\left(12x-5\right)\left(4x-1\right)\left(3x-7\right)\left(1-16x\right)=81\)

\(\Rightarrow\left(48x^2-12x-20x+5\right)\left(3x-7\right)\left(1-16x\right)=81\)

\(\Rightarrow\left(48x^2-32x+5\right)\left(3x-7\right)\left(1-16x\right)=81\)

\(\Rightarrow\left(144x^3-336x^2-96x^2+224x+15x-35\right)\left(1-16x\right)=81\)

\(\Rightarrow\left(144x^3-432x^2+239x-35\right)\left(1-16x\right)=81\)

\(\Rightarrow144x^3-2304x^4-432x^2+6912x^3+239x-3824x^2-35+560x=81\)

\(\Rightarrow-2304x^4+7056x^3-4256x^2+799x-116=0\)

\(\Rightarrow\left[{}\begin{matrix}x_1\approx2,3\\x_2\approx0,5\end{matrix}\right.\)

(12x - 5)(4x - 1) + (3x - 7)(1 - 16x) = 81

48x² - 32x + 5 - 48x + 115x - 7     = 81

83x - 2                                        = 81

83x                                             = 83

=> x                                           = 1

Sửa lại dòng 2 : 48x² - 32x + 5 - 48x² + 115x - 7 = 81

(12x-5).(4x-1)+(3x-7).(1-16x) = 81

  => 48x²-12x-20x+5+3x-48x²-7+112x = 81

  => 83x-2 = 81

  => 83x    = 81+2

  => 83x    = 83

  => x        = 83:83

 => x         = 1 

\(\left(12x-5\right)\left(4x-1\right)+\left(3x-7\right)\left(1-16x\right)=81\)

\(\text{⇔}48x^2-32x+5-48x^2-7+115x=81\)

\(\text{⇔}83x-2=81\)

\(\text{⇔}83x=83\)

\(\text{⇔}x=1\)

Vậy: x=1

Ta có: \(\left(12x-5\right)\left(4x-1\right)+\left(3x-7\right)\left(1-16x\right)=81\)

\(\Leftrightarrow48x^2-12x-20x+5+3x-48x^2-7+112x=81\)

\(\Leftrightarrow83x=83\)

hay x=1

\(\left(12x-5\right)\left(4x-1\right)+\left(3x-7\right)\left(1-16x\right)=81\)

\(\Leftrightarrow48x^2-32x+5+48x^2+115x-7=81\)

\(\Leftrightarrow83x=83\)

\(\Leftrightarrow x=1\)

\(\Leftrightarrow48x^2-12x-20x+5+3x-48x^2-7+112x=81\\ \Leftrightarrow83x=83\Leftrightarrow x=1\)

\(\left(12x-5\right)\left(4x-1\right)+\left(3x-7\right)\left(1-16x\right)=81\)

\(48x^2-12x-20x+5+3x-48x^2-7+112x=81\)

\(83x-2=81\)

\(83x=83\)

\(x=1\)

Rút gọn vế trái:

VT = (12x – 5)(4x – 1) + (3x – 7)(1 – 16x)

     = 12x.(4x – 1) + (–5).(4x – 1) + 3x.(1 – 16x) + (–7).(1 – 16x)

     = 12x.4x+ 12x.(–1) + (–5).4x + (–5).(–1) + 3x.1 + 3x.(–16x) + (–7).1 + (–7).(–16x)

     = 48x2 – 12x – 20x + 5 + 3x – 48x2 – 7 + 112x

     = (48x2 – 48x2) + (– 12x – 20x + 3x + 112x) + (5 – 7)

     = 83x – 2

Vậy ta có:

83x – 2 = 81

       83x = 81 + 2

       83x = 83

           x = 83 : 83

           x = 1.

(12x - 5)(4x - 1) + (3x - 7)(1 - 16x) = 81

<=> 48x² - 12x - 20x + 5 + 3x - 48x² - 7 + 112x = 81

<=> 48x² - 48x² - 12x - 20x + 3x + 112x = 81 - 5 + 7

<=> 83x = 83

<=> x = 1