2(x + 7) - (2x + 3).(x - 1) - 8 = 6x

<=> (2x + 14) - (2x + 3)(x - 1) - 8 - 6x = 0 

<=> 2x + 14 - (2x² + 3x - 2x - 3) - 8 - 6x = 0 

<=> 2x + 14 - (2x² + x - 3) - 8 - 6x = 0 

<=> 2x + 14 - 2x² - x + 3 - 8 - 6x  = 0 
<=> -2x² - 5x + 6 = 0 

<=> 2x² + 5x - 6 = 0

<=> \(x^2+\frac{5}{2}x-3=0\)

\(\Leftrightarrow x^2+2.x.\frac{5}{4}+\frac{25}{16}-\frac{73}{16}=0\)

\(\Leftrightarrow x^2+2.x.\frac{5}{4}+\frac{25}{16}=\frac{73}{16}\)

\(\Leftrightarrow\left(x+\frac{5}{4}\right)^2=\frac{73}{16}\)

\(\Leftrightarrow\orbr{\begin{cases}x+\frac{5}{4}=\frac{73}{16}\\x+\frac{5}{4}=-\frac{73}{16}\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}x=\frac{73}{16}-\frac{5}{4}\\x=-\frac{73}{16}-\frac{5}{4}\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}x=\frac{53}{16}\\x=-\frac{93}{16}\end{cases}}\)

2(x+7)-(2x+3)(x-1)-8=6x

\(\Leftrightarrow2x+14-2x^2+2x-3x+3-8=6x\) 

\(\Leftrightarrow\) \(-2x^2+2x+2x-3x+3-8+14=6x\)

\(\Leftrightarrow-2x^2+x+9=6x\)

\(\Leftrightarrow-2x^2-5x+9=0\)

\(\Leftrightarrow\left(x-\left(\frac{-5+\sqrt{97}}{4}\right)\right)\left(x+\left(\frac{-5-\sqrt{97}}{4}\right)\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}x-\frac{-5+\sqrt{97}}{4}=0\\x+\frac{-5-\sqrt{97}}{4}=0\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}x=\frac{-5+97}{4}\\x=\frac{5-\sqrt{97}}{4}\end{cases}}\)

bn @At the speen of light 

Ở chỗ <=>2x²-5x+6

sai kìa :14+3-8=9 mà

b) \(\frac{3\left(2x+1\right)}{4}-\frac{5x+3}{6}+\frac{x+1}{3}=\frac{x+7}{12}\)

<=> \(\frac{13\left(x+1\right)}{12}-\frac{5x+3}{6}=\frac{x+7}{12}\)

<=> 13(x + 1) - 2(5x + 3) = x + 7

<=> 13x + 13 - 10x - 6 = x + 7

<=> 3x + 7 = x + 7

<=> 3x + 7 - x = 7

<=> 2x + 7 = 7

<=> 2x = 7 - 7

<=> 2x = 0

<=> x = 0

c) 2x + 4(x - 2) = 5

<=> 2x + 4x - 8 = 5

<=> 6x - 8 = 5

<=> 6x = 5 + 8

<=> 6x = 13

<=> x = 13/6

1) 2x – (3 – 5x) = 4( x +3)

<=>2x-3+5x=4x+12

<=>2x-3+5x-4x-12=0

<=>3x-15=0

<=>x=5

2) 5(2x-3) - 4(5x-7) =19 - 2(x+11)

<=>10x-15-20x+28=19-2x-22

<=>10x-15-20x+28-19+2x+22=0

<=>-8x+16=0

<=>x=2

tham khảo

1) 2x – (3 – 5x) = 4( x +3)

<=>2x-3+5x=4x+12

<=>2x-3+5x-4x-12=0

<=>3x-15=0

<=>x=5

2) 5(2x-3) - 4(5x-7) =19 - 2(x+11)

<=>10x-15-20x+28=19-2x-22

<=>10x-15-20x+28-19+2x+22=0

<=>-8x+16=0

<=>x=2

b/ (x² + x + 1)(x⁶ - x⁴ + x³ - x + 1)

c/ (x - 1)(2x³ + 1)

d/ (2x² + 6x + 5)(2x² - 6x + 5)

Ta có : x² - 2x - (x + 3)² = 6

<=> x² - 2x - x² - 6x - 9 = 6

<=> -8x - 9 = 6 

=> -8x = 15

=> x = \(\frac{15}{-8}\)

a)   1,2 - ( x - 0,8 ) = -2( 0,9+ x ) 

<=> 1,2 -  x + 0,8  = -1.8 - 2x  

<=> x = -3,8

Vậy x = -3,8

b)   2,3x - 2(0,7 + 2x ) = 3,6 - 1,7x 

<=>  2,3x - 1,4 - 4x  = 3,6 - 1,7x 

<=>  -3,4x = 5

<=>  x = \(\dfrac{-25}{17}\)

Vậy x = \(\dfrac{-25}{17}\)

c)    3(2,2 - 0,3x ) = 2,6 + (0,1x - 4 ) 

<=> 6,6 - 0,9x = 2,6 + 0,1x - 4

<=> -x = -8

<=> x = 8

Vậy x = 8

d)    3,6 - 0,5(2x + 1) = x- 0,25(2-4x)

<=> 3,6 - x - 0.5 = x - 0,5 + x

<=> -3x = -3,6

<=>  x = 1.2

Vậy x = 1.2

2)     => X/3 = Y/4

(2X^2 + Y^2)/(2.3^2 + 4^2) =  136/34 = 4

2X^2 = 4.18 = 72 => x  = 6

y^2 = 4.16 = 64 => y = 8

5)  (a+2b-3c)/(2+2.3 - 3.4) =  20/4 = 5

a = 10

2b = 30 => b = 15

3c = 60 => c = 20 

kho hieu qua 

18 voi 16 lay dau ra vay