`2)x^4+2x^3-x^2-2x+1=0`

`<=>x^4+2x^3+x^2-2x^2-2x+1=0`

`<=>(x^2+x)^2-2(x^2+x)+1=0`

`<=>(x^2+x-1)^2=0`

`<=>x^2+x-1=0`

`\Delta=1+4=5`

`=>x_{1,2}=(-1+-sqrt5)/2`

Vậy `S={(-1+sqrt5)/2,(-1+sqrt5)/2`

`3)x^4-4x^3-9x^2+8x+4=0`

`<=>x^4-x^3-3x^3+3x^2-12x^2+12x-4x+4=0`

`<=>(x-1)(x^3-3x^2-12x-4)=0`

`<=>(x-1)(x^3+2x^2-5x^2-10x-2x-4)=0`

`<=>(x-1)(x+2)(x^2-5x-10)=0`

`+)x=1`

`+)x=-2`

`+)x^2-5x-10=0`

`Delta=25+40=65`

`=>x_{12}=(5+sqrt{65})/2`

\(|-2x+1,5|=\dfrac{1}{4}\Rightarrow-2x+1,5=\pm\dfrac{1}{4}\)

\(-2x+1,5=\dfrac{1}{4}\Rightarrow-2x=1,5-0,25\Rightarrow-2x=1,25\Rightarrow x=1,25:\left(-2\right)\Rightarrow x=...\)

\(-2x+1,5=-\dfrac{1}{4}\Rightarrow-2x=-0,25-1,5\Rightarrow-2x=1,75\Rightarrow x=1,75:\left(-2\right)\Rightarrow x=...\)

\(\dfrac{3}{2}-|1.\dfrac{1}{4}+3x|=\dfrac{1}{4}\Rightarrow|1.\dfrac{1}{4}+3x|=\dfrac{3}{2}-\dfrac{1}{4}\Rightarrow|1.\dfrac{1}{4}+3x|=\dfrac{5}{4}\)

\(\Rightarrow1.\dfrac{1}{4}+3x=\pm\dfrac{5}{4}\)

\(1.\dfrac{1}{4}+3x=\dfrac{5}{4}\Rightarrow\dfrac{1}{4}+3x=\dfrac{5}{4}\Rightarrow3x=\dfrac{5}{4}-\dfrac{1}{4}\Rightarrow3x=1\Rightarrow x=3\)

\(1.\dfrac{1}{4}+3x=-\dfrac{5}{4}\Rightarrow\dfrac{1}{4}+3x=-\dfrac{5}{4}\Rightarrow3x=-\dfrac{5}{4}-\dfrac{1}{4}\Rightarrow3x=-\dfrac{3}{2}x=...\)

Bài 2:

\(\left(5x+1\right)^2-\left(2xy-3\right)^2\)

\(=25x^2+10x+1-\left(2xy-3\right)^2\)

\(=25x^2+10x+1\left(4x^2y^2-12xy+9\right)\)

\(=25x^2+10x+1-4x^2y^2+12xy-9\)

\(=25x^2-4x^2y^2+10x+12xy-8\)

Bài 2: 

\(\left(x-1\right)\left(x^2+x+1\right)=x^2\left(x-9\right)+2x+6\)

\(=x^3-1=x^3-9x^2+2x+6\)

\(=x^3-9x^2+2x+6=x^3-1\)

\(=x^3-9x^2+2x+6+1=x^3-1+1\)

\(=x^3-9x^2+2x+7=x^3\)

\(=x^3-9x^2+2x+7-x^3=x^3-x^3\)

\(=-9x^2+2x+7=0\)

\(\Rightarrow x=-\frac{7}{9};x=1\)

c: \(\Leftrightarrow6x+3=\dfrac{11}{4}\left(2-x\right)\)

\(\Leftrightarrow x=\dfrac{10}{11}\)

tách nhỏ câu hỏi ra

1. -3(-x+3)

= 3x - 6

2. -5x³ (-3x + 5)

= 15x⁴ - 25x³

3. -2x (-2x - 6)

= 4x² + 12x

\(Đk:\) \(x\ne1,x\ne2,x\ne3\)

\(\Rightarrow\dfrac{x+4}{\left(x-2\right)\left(x-1\right)}+\dfrac{x+1}{\left(x-3\right)\left(x-1\right)}=\dfrac{2x+5}{\left(x-3\right)\left(x-1\right)}\)

\(\Rightarrow\dfrac{\left(x+4\right)\cdot\left(x-3\right)+\left(x+1\right)\left(x-2\right)}{\left(x-2\right)\left(x-1\right)\left(x-3\right)}=\dfrac{\left(2x+5\right)\left(x-2\right)}{\left(x-3\right)\left(x-1\right)\left(x-2\right)}\)

\(\Rightarrow x^2-3x+4x-12+x^2-2x+x-2=2x^2-4x+5x-10\)

\(\Rightarrow0x-14=x-10\)

\(\Rightarrow x=-4\left(tmđk\right)\)

Bn thông cảm.Bài này mn ko bt làm

a) 4( 18 - 5x ) - 12( 3x - 16 ) = 15( 2x - 16 ) - 6( x + 14 )

<=> 72 - 20x - 36x + 192 = 30x - 240 - 6x - 84

<=> -20x - 36x - 30x + 6x = -240 - 84 - 72 - 192

<=> -80x = -588

<=> x = -588/-80 = 147/20

b) ( x + 3 )( x + 2 ) - ( x - 2 )( x + 5 ) = 6

<=> x² + 5x + 6 - ( x² + 3x - 10 ) = 6

<=> x² + 5x + 6 - x² - 3x + 10 = 6

<=> 2x + 16 = 6

<=> 2x = -10

<=> x = -5

c) -x( x + 3 ) + 2 = ( 4x + 1 )( x - 1 ) + 2x

<=> -x² - 3x + 2 = 4x² - 3x - 1 + 2x

<=> -x² - 3x - 4x² + 3x - 2x = -1 - 2

<=> -5x² - 2x = -3

<=> -5x² - 2x + 3 = 0

<=> -( 5x² + 2x - 3 ) = 0

<=> -( 5x² + 5x - 3x - 3 ) = 0

<=> -[ 5x( x + 1 ) - 3( x + 1 ) ] = 0

<=> -( x + 1 )( 5x - 3 ) = 0

<=> \(\orbr{\begin{cases}x+1=0\\5x-3=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=-1\\x=\frac{3}{5}\end{cases}}\)

d) ( 2x + 3 )( x - 3 ) - ( x - 3 )( x + 1 ) = ( 2 - x )( 3x + 1 ) + 3 

<=> 2x² - 3x - 9 - ( x² - 2x - 3 ) = -3x² + 5x + 2 + 3

<=> 2x² - 3x - 9 - x² + 2x + 3 = -3x² + 5x + 2 + 3

<=> 2x² - 3x - x² + 2x + 3x² - 5x = 2 + 3 + 9 - 3

<=> 4x² - 6x = 11

<=> 4x² - 6x - 11 = 0

=> Vô nghiệm ( Lớp 8 chưa học nghiệm vô tỉ nên để vậy ) :))

vẫn làm được nha quỳnh !

\(4x^2-6x-11=0\)

\(< =>\left(4x^2-6x+\frac{9}{4}\right)-13\frac{1}{4}=0\)

\(< =>\left(2x-\frac{3}{2}\right)^2=\frac{53}{4}\)

\(< =>\orbr{\begin{cases}2x-\frac{3}{2}=\frac{\sqrt{53}}{2}\\2x-\frac{3}{2}=-\frac{\sqrt{53}}{2}\end{cases}}\)

\(< =>\orbr{\begin{cases}2x=\frac{3+\sqrt{53}}{2}\\2x=\frac{3-\sqrt{53}}{2}\end{cases}}\)

\(< =>\orbr{\begin{cases}x=\frac{3+\sqrt{53}}{4}\\x=\frac{3-\sqrt{53}}{4}\end{cases}}\)

c. - x ( x + 3 ) + 2 = ( 4x + 1 ) ( x - 1 ) + 2x

<=> - x² - 3x + 2 = 4x² - x - 1

<=> 4x² - x - 1 + x² + 3x - 2 = 0

<=> 5x² + 2x - 3 = 0

<=> ( 5x² + 5x ) - ( 3x + 3 ) = 0

<=> 5x ( x + 1 ) - 3 ( x + 1 ) = 0

<=> ( 5x - 3 ) ( x + 1 ) = 0 

\(\Leftrightarrow\orbr{\begin{cases}5x-3=0\\x+1=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=\frac{3}{5}\\x=-1\end{cases}}\)

d. ( 2x + 3 ) ( x - 3 ) - ( x - 3 ) ( x + 1 ) = ( 2 - x ) ( 3x + 1 ) + 3

<=> ( x - 3 ) ( 2x + 3 - x - 1 ) = - 3x² + 5x + 5

<=> x² - x - 6 = - 3x² + 5x + 5

<=>  - 3x² + 5x + 5 - x² + x + 6 = 0

<=> - 4x² + 6x + 11 = 0

\(\Leftrightarrow x=\frac{6\pm\sqrt{\left(-6\right)^2-4\left(4.\left(-11\right)\right)}}{2.4}\)( xài công thức bậc 2 )

\(\Leftrightarrow x=\frac{6\pm2\sqrt{53}}{8}\Leftrightarrow x=\frac{3\pm\sqrt{53}}{4}\)

Vậy \(x=\frac{3+\sqrt{53}}{4};x=\frac{3-\sqrt{53}}{4}\)