[ -3x +21 ] [ 5 .| x | - 15 ] =0

<=> (-3x+21)=0 hoặc (5|x|-15)=0

<=> x=7 hoặc |x|=3

<=> x={7;-3;3}

a,2x-(-17)=15

2x+17=15

2x=15-17

2x=-2

=>x=-1

a, 2x -(-17) = 15

2x + 17 = 15 

2x        = 15 - 17 

2x        =(-2)

 x         = (-2) : 2 

x          = (-1)

a ) 2x - 1 = 7

     2x        = 7 + 1

      2x         = 8

        x         = 8 : 2

        x         = 4

b ) 3 ( x + 5 ) = 21

         ( x + 5 ) = 21 : 3

         ( x + 5 ) = 7

            x         = 2

c ) 20 - ( 3x - 1 ) = 15

             ( 3x - 1 ) = 20 - 15

             ( 3x - 1 ) = 5

                3x        = 6

                  x         = 2

d ) ( x - 135 ) -120 = 0

      ( x - 135 )          = 120

       x                        = 120  + 135

       x                        = 255

a)2x - 1 = 7

=>2x=8

=>x=4

b) 3(x+5) = 21

=>x+5=7

=>x=2

c) 20 - (3x - 1) = 15

=>3x-1=5

=>3x=6

=>x=2

d) (x  - 135) - 120 = 0

=>x-135=120

=>x=155

phần d chỗ cuối sửa thành 255 nhé

**** ko z, t đag cần 

a) 7x+4=3x+16\(\Leftrightarrow\)4x=12\(\Leftrightarrow\)x=3

b)(x+9)(3x-15)=0\(\Leftrightarrow\)x+9=0 hoặc 3x-15=0

\(\Rightarrow\)x\(\in\){-9;5}

c) |-5x|=2x+21

Nếu x\(\le\)0 thì -5x=2x+21\(\Leftrightarrow\)x=-3 (t/m)

Nếu x>0 thì -5x=-2x-21\(\Leftrightarrow\)x=7 (t/m)

Vậy x\(\in\){-3;7}

d) 3x-5>15-x\(\Leftrightarrow\)4x>20\(\Leftrightarrow\)x>5

e) \(\dfrac{x+1}{2001}+\dfrac{x+5}{2005}< \dfrac{x+9}{2009}+\dfrac{x+13}{2013}\)

\(\Leftrightarrow\dfrac{x+1}{2001}-1+\dfrac{x+5}{2005}-1< \dfrac{x+9}{2009}-1+\dfrac{x+13}{2013}-1\)

\(\Leftrightarrow\)\(\dfrac{x-2000}{2001}+\dfrac{x-2000}{2005}-\dfrac{x-2000}{2009}-\dfrac{x-2000}{2013}< 0\)

\(\Leftrightarrow\)(x-2000)(\(\dfrac{1}{2001}+\dfrac{1}{2005}-\dfrac{1}{2009}-\dfrac{1}{2013}\))<0

Vì \(\dfrac{1}{2001}+\dfrac{1}{2005}-\dfrac{1}{2009}-\dfrac{1}{2013}>0\) nên x-2000<0

\(\Leftrightarrow\)x<2000

Rút gọn hết ta được :

a/ 41x - 17 = -21

=> 41x = -4 => x = 4/41

b/ 34x - 17 = 0 

=> 34x = 17

=> x = 17/34 = 1/2

c/ 19x + 56 = 52 

=> 19x = -4

=> x = -4/19

d/ 20x² - 16x - 34 = 10x² + 3x - 34

=> 10x² - 19x = 0

=> x(10x - 19) = 0

=> x = 0 

hoặc 10x - 19 = 0 => 10x = 19 => x = 19/10

Vậy x = 0 ; x = 19/10

Rút gọn hết ta được :

a/ 41x - 17 = -21

=> 41x = -4 => x = 4/41

b/ 34x - 17 = 0

=> 34x = 17

=> x = 17/34 = 1/2

c/ 19x + 56 = 52

=> 19x = -4

=> x = -4/19

d/ 20x 2 - 16x - 34 = 10x 2 + 3x - 34

=> 10x 2 - 19x = 0

=> x(10x - 19) = 0

=> x = 0 hoặc 10x - 19 = 0

=> 10x = 19

=> x = 19/10

Vậy x = 0 ; x = 19/10 

a) ( 6x - 3 ) ( 2x + 4 ) + ( 4x - 1 ) ( 5 - 3x ) = -21

<=> 12x² + 24x - 6x - 12 + 20x - 12x² - 5 + 3x = -21

<=> 41x = -21 + 12 + 5 

<=> 41x = -4

<=> x = -4/41

a: \(\Leftrightarrow x^2+10x+25-x^2+4x=55\)

=>14x=30

hay x=15/7

b: \(\Leftrightarrow\left(x-7\right)\left(x-3\right)=0\)

hay \(x\in\left\{7;3\right\}\)