a) <=> 15-5x-20=-12-3

<=> -5x=-12-3-15+20=-10

=>x=-10:(-5)=2

b)<=>7-x-25-7=-25

<=> -x=-25-7+25+7=0 =>x=0

c) /x+2/=0 => x+2=0 =>x=-2

d) sai đề

e)<=> /x-5/ = 7

<=> \(\orbr{\begin{cases}x-5=7\\x-5=-7\end{cases}}\)

<=> \(\orbr{\begin{cases}x=12\\x=-2\end{cases}}\)

g) <=> -x-20-8+2x=-15

<=> x=-15+20+8=13

d là | x + 3 | = 7 - ( - 2 )

Áp dụng tính chất của dãy tỷ số bằng nhau

\(\frac{3x-1}{40-5x}=\frac{25-3x}{4x-34}=\frac{\left(3x-1\right)+\left(25x-3x\right)}{\left(40-5x\right)+\left(5x-34\right)}=4\)

\(\Rightarrow\frac{3x-1}{40-5x}=4\)

\(\Rightarrow3x-1=3\left(40-5x\right)\)

\(\Rightarrow3x-1=160-20x\)

\(\Rightarrow23x=161\)

\(\Rightarrow x=161:23\)

\(\Rightarrow x=7\)

dễ thương quá minion 

d, X/8*32+X/3*18-X/5*10=120

   X*32/8+X*18/3-X*10/5=120

  32X/8+18X/3-10X/5=120

  4X+6X-2X=120

  8X=120

 X=120/8

X=15

a, ( 25 * 12 - X - 25 ) : 25 = 4

( 25 * 12 - x - 25 )           = 4 * 25 

( 25 * 12 - x - 25 )           = 100

300 - x - 25                    = 100

300 - x                           = 100 + 25

300 - x                           = 125

x                                   = 300 - 125

x                                   = 175

x - 5 + 25 = 13

x - 30 = 13

x =13 +30

x =43

x-5+25=5+8

x-5+25=13

x-30  =13

x=43

mik ko chac lam neu dung tick mik vs

x:3/5=25/4-2

x:3/5=17/4

x=17/4.3/5

x=51/20

2+ x : 3/ 5 = 25 / 4

2+ x =25/4x3/5

2+x=15/4

x=15/4-2

x=7/4

Tìm x:

\(2+x:\dfrac{3}{5}=\dfrac{25}{4}\)

\(x:\dfrac{3}{5}=\dfrac{25}{4}-2\)

\(x:\dfrac{3}{5}=\dfrac{17}{4}\)

\(x=\dfrac{17}{4}\)x\(\dfrac{3}{5}\)

\(x=\dfrac{51}{20}\).

Ta có ; x² - 25 - (x + 5) = 0

=> x² - 5² - (x + 5) = 0

=> (x - 5) (x + 5) - (x + 5) = 0

=> (x + 5) (x - 6) = 0

\(\Leftrightarrow\orbr{\begin{cases}x+5=0\\x-6=0\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}x=-5\\x=6\end{cases}}\)