a, x+15=20-4x

=> x + 4x = 20 - 15

=> 5x = 5

=> x = 5 : 5

=> x = 1

b, 17-x=7-6x

=> -x + 6x = 7 - 17

=> 5x = - 10

=> x = -10 : 5

=> x = -2

c, 4.(x-5)-3.(x+7)= -19

=> 4x - 4.5 - 3.x + 3.7 = -19

=> 4x - 20 - 3x + 21 = -19

=> (4x-3x) + (21-20) = -19

=> 1x + 1 = -19

=> x = -19 - 1

=> x = -18

d, -7.(5-x)-2.(x-10)=15

=> -7x - (-7).5 - 2x - 2.10 = 15

=> -7x - (-35) - 2x - 20 = 15

=> -7x + 35 - 2x - 20 = 15

=> -7x+2x + (35-20) = 15

=> -5x + 15 = 15

=> -5x = 15 - 15

=> -5x = 0

=> x = 0 : (-5)

=> x = 0

e, -5.(2-x)+4.(x-3) = 10.x-15

=> -5x - (-5).2 + 4x - 4.3 = 10x - 15

=> -5x - (-10) + 4x - 12 = 10x - 15

=> -5x + 10 + 4x - 12 = 10x - 15

=> (-5x+4x) - (12-10) = 10x - 15

=> -1x - 2 = 10x - 15

=> -1x - 10x = -15 + 2

=> -11x = -13

=> x = \(\frac{-13}{-11}\)

8 - | x + 2 | = 5 

     | x + 2 | = 8 - 5 

     | x + 2 | = 3 

       x          = 3 - 2 

       x          = 1 

16 - ( -x + 33 ) = 11 

        ( -x + 33 ) = 16 - 11 

        ( -x + 33 ) = 5 

          -x            = 5 - 33 

          -x            = -28 

( x + 17 ) - 12 = 18 

( x + 17 )         = 18 + 12 

( x + 17 )         = 30 

  x                     = 30 - 17 

  x                     = 13 

k mink nha! 

\(\frac{x}{8}=\frac{-2}{5}\cdot\frac{3}{16}\)

\(\frac{x}{8}=\frac{-3}{40}\)

\(\Rightarrow x=\frac{8.\left(-3\right)}{40}=\frac{-3}{5}\)

\(\frac{x+4}{5}=\frac{-1}{7}\cdot\frac{14}{15}\)

\(\frac{x+4}{5}=\frac{-2}{15}\)

\(\Rightarrow x+4=\frac{5.\left(-2\right)}{15}=\frac{-2}{3}\)

\(\Rightarrow x=\frac{-14}{3}\)

giải thích đầy đủ hộ mik với ạk

\(\left(x-2\right)\left(x^2+2x+4\right)+3x-4=\left(x+2\right)\left(x^2-2x+4\right)-x+1\)

\(\Rightarrow\left(x^3-8\right)+3x-4=\left(x^3+8\right)-x+1\)

\(\Rightarrow x^3-8+3x-4=x^3+8-x+1\)

\(\Rightarrow x^3-x^3+3x+x=8+8+4+1\)

\(\Rightarrow4x=21\)

\(\Rightarrow x=\dfrac{21}{5}\)

Bài 2: 

a: Ta có: \(x^2+4x+7\)

\(=x^2+4x+4+3\)

\(=\left(x+2\right)^2+3\ge3\forall x\)

Dấu '=' xảy ra khi x=-2

a) \(3\frac{1}{3}\left(3\frac{1}{4}+2x\right)=6\frac{2}{3}\)

   \(3\frac{1}{3}\times3\frac{1}{4}+2x=6\frac{2}{3}\)

   \(10\frac{5}{6}+2x=6\frac{2}{3}\)

   \(2\times x=6\frac{2}{3}+10\frac{5}{6}=17,5\)

   \(x=17,5\div2=8,75\)

Vậy x = 8,75

b) \(x-25\%x=\frac{6}{11}\left(\frac{1}{2}+\frac{3}{4}-\frac{1}{3}\right)\)

   \(x-\frac{25}{100}x=\frac{6}{11}\left(\frac{1}{2}+\frac{3}{4}-\frac{1}{3}\right)\)

   \(x-\frac{1}{4}\times x=\frac{6}{11}\times1\frac{7}{12}=\frac{19}{22}\)

   \(x\times x=\frac{19}{22}+\frac{1}{4}=\frac{49}{44}\)

\(\Rightarrow2x\left(x\times x\right)=\frac{49}{44}\)   

   \(x=\frac{49}{44}\div2=\frac{49}{88}\)

   Vậy x = \(\frac{49}{88}\)

c) \(\left(4,5-2x\right)\times1\frac{4}{7}=\frac{11}{14}\)

   \(4,5-2x\times1\frac{4}{7}=\frac{11}{14}\)

   \(-2x\times1\frac{4}{7}=\frac{11}{14}-4,5=-3\frac{5}{7}\)

   \(-2\times x=-3\frac{5}{7}\div1\frac{4}{7}=-2\frac{4}{11}\)

   \(x=-2\frac{4}{11}\div\left(-2\right)=1\frac{2}{11}\)

Vậy x = \(1\frac{2}{11}\)

d) \(-3^2-|2x+3|=4\)

    \(9-|2x+3|=4\)

   \(-|2x+3|=4-9=-5\)

   \(-|2x|=-5-|3|=-8\)

   \(-|x|=-8\div2=-4\)

    \(-x=4\Rightarrow x=-4\)

   Vậy x = -4 (-x được xem là số đối của x)