a) => 6x-6-5x=15

=> 6x-6+6-5x=15+6

=> 6x-5x=21

=> x=21

b) => 8x-4-7x=16

=> 8x-4+4-7x=16+4

=> 8x-7x=20

=> x=20

c) => 8-[-(2.4x)]-9x-21=31

=> 8-(-8x)-9x=31+21

=> 8-(-8x)-9x=52

=> (-8x)-9x=8-52

=> (-8x)+(-9x)=-44

=> -17x=-44

=> x=(-44):(-17)

=> x=

câu c chắc tớ làm sai

a) x = 21

b) x = 20

c) x = -4

21

20

4

tic nha

16-2x=40-3x

40-16=3x-2x

24=x

x=24

2x-16=40+x

  2x-x=40+16

      x=56

tick nhé cảm ơn

(x-7)(x+2005) = 0

\(\Rightarrow\) x-7 = 0

Vậy x = 7

2x-16=40+x=>x=56

16-2x=40-3x=>x=24

2(4x-2x)-7x=16=>x=-5,(3)

-2(-3-4x)-3(3x+7)=31=>x=-46

9(x+4)-4(2x+15)=3=>x=27

-2[x+(-7)]+(x-3)=12=>x=-1

(x-7)(x+2005)=0 =>x=7;-2005

Bài 1 :                                         Bài giải

\(-2\left(-3-4x\right)-3\left(3x-7\right)=31\)

\(6+8x-9x-21=31\)

\(-x-15=31\)

\(-x=31+15\)

\(-x=46\)

\(x=-46\)

b, \(10\left(x-7\right)=8\left(x-4\right)+x\)

\(10x-70=8x-32+x\)

\(10x-70=9x-32\)

\(10x-9x=-32+70\)

\(x=38\)

c, \(2\left|x-1\right|=3\cdot\left(5-1\right)\)

\(2\left|x-1\right|=15-3\)

\(2\left|x-1\right|=12\)
\(\left|x-1\right|=12\text{ : }2\)

\(\left|x-1\right|=6\)

\(\Rightarrow\orbr{\begin{cases}x-1=-6\\x-1=6\end{cases}}\Rightarrow\orbr{\begin{cases}x=-5\\x=7\end{cases}}\)

\(\Rightarrow\text{ }x\in\left\{-5\text{ ; }7\right\}\)

d, \(2\left(x+3\right)-2\left(x-3\right)=x\)

\(2\left(x+3-x-3\right)=x\)

\(2\cdot0=x\)

\(x=0\)

e, \(\left(x+3\right)\left(x-4\right)=0\)

\(\Rightarrow\orbr{\begin{cases}x+3=0\\x-4=0\end{cases}}\Rightarrow\orbr{\begin{cases}x=-3\\x=4\end{cases}}\)

\(\Rightarrow\text{ }x\in\left\{-3\text{ ; }4\right\}\)

a, \(-2\left(-3-4x\right)-3\left(3x-7\right)=31\)

\(6+8x-9x-21=31\)

\(-x-15=31\)

\(-x=31+15\)

\(-x=46\)

\(x=-46\)

b, \(10\left(x-7\right)=8\left(x-4\right)+x\)

\(10x-70=8x-32+x\)

\(10x-70=9x-32\)

\(10x-9x=-32+70\)

\(x=38\)

c, \(2\left|x-1\right|=3\cdot\left(5-1\right)\)

\(2\left|x-1\right|=15-3\)

\(2\left|x-1\right|=12\)
\(\left|x-1\right|=12\text{ : }2\)

\(\left|x-1\right|=6\)

\(\Rightarrow\orbr{\begin{cases}x-1=-6\\x-1=6\end{cases}}\Rightarrow\orbr{\begin{cases}x=-5\\x=7\end{cases}}\)

\(\Rightarrow\text{ }x\in\left\{-5\text{ ; }7\right\}\)

d, \(2\left(x+3\right)-2\left(x-3\right)=x\)

\(2\left(x+3-x-3\right)=x\)

\(2\cdot0=x\)

\(x=0\)

e, \(\left(x+3\right)\left(x-4\right)=0\)

\(\Rightarrow\orbr{\begin{cases}x+3=0\\x-4=0\end{cases}}\Rightarrow\orbr{\begin{cases}x=-3\\x=4\end{cases}}\)

\(\Rightarrow\text{ }x\in\left\{-3\text{ ; }4\right\}\)

185 ban co the ung ho minh bang cach tick

=>[6-(-8x)]-(9x-210)=31

=>6-(-8x)-9x+210=31

=>(6+210)-(-8x+9x)=31

=>216-x=31

=>x=216-31

=>x=185

-2.(-3-4x)-3(3x-70)=31

6+8x-9x+210=31

-1x+216=31

-1x=-185

=> x=185

c: Ta có: \(x^3+3x^2+3x-7=0\)

\(\Leftrightarrow x+1=2\)

hay x=1

b: Ta có: \(x\left(x-3\right)-4x+12=0\)

\(\Leftrightarrow\left(x-3\right)\left(x-4\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=3\\x=4\end{matrix}\right.\)

c: Ta có: \(4x^3-4x^2+x=0\)

\(\Leftrightarrow x\left(2x-1\right)^2=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x=\dfrac{1}{2}\end{matrix}\right.\)

d: Ta có: \(x^3+3x^2+3x-7=0\)

\(\Leftrightarrow x+1=2\)

hay x=1