a) x-12=-9+15

     x-12=24

     x=24+12

     x=36

Vậy x=36

b)4x -12=400

    4x=412

    x=412:4

   x=103

Vậy x=103

c)2x -35=15

   2x=50

   x=50:2

   x=15

Vậy x=15

d)3x+17=2

   3x=-15

   x=(-15):3

  x=-5

Vậy x=-5

e)\(\frac{-5}{8}=\frac{x}{16}\)

\(\Rightarrow\left(-5\right).16=8.x\)

\(\Rightarrow8x=-80\)

\(\Rightarrow x=-10\)

f)\(\frac{y}{10}=-\frac{4}{8}\)

\(\Rightarrow8y=\left(-4\right).10\)

\(\Rightarrow8y=-40\)

\(\Rightarrow y=-5\)

a) x - 12 = -9 + 15 

=> x - 12 = 6 

=> x = 6 + 12 = 18

b) 4x - 12 = 400 

=> 4x = 400 + 12 = 412

=> x = 412 : 4 = 103

c) 2x - 35 = 15

=> 2x = 15 + 35 = 50

=> x = 50 : 2 = 25

d) 3x + 17 = 2

=> 3x = 2 - 17 

=> 3x = -15

=> x = -15 : 3 = -5

e) \(\frac{-5}{8}=\frac{x}{16}\)

\(=>\frac{-10}{16}=\frac{x}{16}\)

=> x = -10

f) \(\frac{y}{10}=\frac{-4}{8}\)

\(=>\frac{y}{10}=\frac{-1}{2}\)

\(=>\frac{y}{10}=\frac{-5}{10}\)

=> y = -5

\(\left(4x+1\right)\left(x-3\right)-\left(x-7\right)\left(4x-1\right)=15\\ \Leftrightarrow4x^2+x-12x-3-\left(4x^2-28x-x+7\right)-15=0\\ \Leftrightarrow4x^2-11x-3-4x^2+29x-7-15=0\\ \Leftrightarrow18x=25\\ \Leftrightarrow x=\dfrac{25}{18}\)

Vậy \(x=\dfrac{25}{18}\)

Lời giải:

$(4x+1)(x-3)-(x-7)(4x-1)=15$

$\Leftrightarrow (4x^2-11x-3)-(4x^2-29x+7)=15$

$\Leftrightarrow 18x-10=15$

$\Leftrightarrow 18x=25$

$\Leftrightarrow x=\frac{25}{18}$