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18 tháng 6 2016

a/ 4x(7x - 5) - 7x(4x - 2) = -12

  => 28x2 - 20x - 28x2 + 14x = -12

  => -6x = -12

  => x = 2

b/ (x + 3)(x - 2) + 3x = 4(x + 3/4) 

  => x2 + x - 6 + 3x - 4x - 3 = 0

  => x2 - 9 = 0

  => x2 = 9

  => x = 3 hoặc x = -3

18 tháng 6 2017

a) \(4x.\left(7x-5\right)-7x\left(4x-2\right)=-12\)

\(\Rightarrow28x^2-20x-28x^2+14x=-12\)

\(\Rightarrow x\left(14-20\right)=-12\)

\(\Rightarrow-6x=12\)

\(\Rightarrow x=-2\)

b) \(3x.\left(2x-4\right)-6x\left(x+5\right)=x-1\)

\(\Rightarrow3x.\left[\left(2x-4\right)-2.\left(x+5\right)\right]=x-1\)

\(\Rightarrow3x.\left(2x-4-2x-10\right)=x-1\)

\(\Rightarrow-42x=x-1\)

\(\Rightarrow-42x-x=-1\)

\(\Rightarrow-43x=-1\)

\(\Rightarrow x=\dfrac{1}{43}\)

18 tháng 6 2017

a, \(4x\left(7x-5\right)-7x\left(4x-2\right)=-12\)

\(\Rightarrow28x^2-20x-28x^2+14=-12\)

\(\Rightarrow-20x=-12-14\)

\(\Rightarrow-20x=-26\Rightarrow x=1,3\)

Vậy \(x=1,3\)

b, \(3x\left(2x-4\right)-6x\left(x+5\right)=x-1\)

\(\Rightarrow6x^2-12x-6x^2-30-x=-1\)

\(\Rightarrow-13x=-1+30\)

\(\Rightarrow-13x=29\Rightarrow x=\dfrac{-29}{13}\)

Vậy \(x=\dfrac{-29}{13}\)

Chúc bạn học tốt!!!

7 tháng 7 2019

a) 4x - 2x + 3 - 4x.(x - 5) = 7x - 3

--> 4x2 - 2x + 3 - 4x2 + 20x = 7x - 3

--> 4x2 - 2x - 4x2 + 20x - 7x = -3 - 3

--> 11x = -6

--> x = \(\frac{-6}{11}\)

b) -3x.(x - 5) + 5.(x - 1) + 3x2 = 4x

--> -3x2 + 15x + 5x - 5 + 3x2 = 4x

--> -3x + 15x + 5x + 3x2 - 4x = 5 

--> 16x = 5

--> x = \(\frac{5}{16}\)

c) 7x.(x - 2) - 5.(x - 1) = 21x2 - 14x2 + 3

--> 7x2 - 14x - 5x + 5 = 7x2 + 3 

--> 7x - 14x - 5x - 7x2  = -5 + 3 

--> -19x = -2 

--> x = \(\frac{2}{19}\)

d) 3.(5x - 1) - x.(x - 2) + x2 - 13x = 7

--> 15x - 3 - x2 + 2x + x2 - 13x = 7

--> 15x - x2 + 2x + x2 - 13x = 3 + 7

--> 4x = 10

--> x = \(\frac{5}{2}\)

e) \(\frac{1}{5}\)x.(10x - 15) - 2x.(x - 5) = 12

--> 2x2 - 3x - 2x2 + 10x = 12

--> 7x = 12

--> x = \(\frac{12}{7}\)

~ Học tốt ~

4 tháng 7 2019

a) 4x2 - 2x + 3 - 4x(x - 5) = 7x - 3

=> 4x2 - 2x + 3 - 4x2 + 20x = 7x - 3

=> 18x + 3 = 7x - 3

=> 18x - 7x = -3 - 3

=> 11x = -6

=>  x = -6/11

b) -3x(x - 5) + 5(x - 1) + 3x2 = 4x

=> -3x2 + 15x + 5x - 5 + 3x2 = 4x

=> 20x - 5 = 4x

=> 20x - 4x = 5

=> 16x = 5

=> x = 5/16

\(c,7x\left(x-2\right)-5\left(x-1\right)=21x^2-14x^2+3\)

\(\Leftrightarrow7x^2-14x-5x+5=7x^2+3\)

\(\Leftrightarrow7x^2-7x^2-19x=3-5\)

\(\Leftrightarrow-19x=-2\)

\(\Leftrightarrow x=\frac{2}{19}\)

4 tháng 7 2019

a) 5.(x^2-3x+1)+x.(1-5x)=x-2

\(\Leftrightarrow5x^2-15x+5+x-5x^2=x-2\)

\(\Leftrightarrow-14x-x=-2-5\)

\(\Leftrightarrow-15x=-7\)

\(\Leftrightarrow x=\frac{7}{15}\)

b\(,3x.\left(\frac{4}{3}+1\right)-4x\left(x-2\right)=10\)

\(\Leftrightarrow4x+3x-4x^2+8x-10=0\)

\(\Leftrightarrow-4x^2+15x-10=0\)

Đề sai???

\(c,12x^2-4x\left(3x-5\right)=10x-17\)

\(\Leftrightarrow12x^2-12x^2+20x-10x=-17\)

\(\Leftrightarrow10x=-17\)

\(\Leftrightarrow x=-\frac{17}{10}\)

\(d,4x\left(x-5\right)-7x\left(x-4\right)+3x^2=12\)

\(\Leftrightarrow4x^2-20x-7x^2+28x+3x^2=12\)

\(\Leftrightarrow8x=12\)

\(\Leftrightarrow x=\frac{3}{2}\)

15 tháng 8 2020

a) \(5x\left(\frac{1}{5}x-2\right)+3\left(6-\frac{1}{3}x^2\right)=12\)

=> \(x^2-10x+18-x^2=12\)

=> -10x + 18 = 12

=> -10x = -6

=> -5x = -3

=> x = 3/5

b) 7x(x - 2) - 5(x - 1) = 7x2 + 3

=> 7x2 - 14x - 5x + 5 = 7x2 + 3

=> 7x2 - 14x - 5x + 5 - 7x2 - 3 = 0

=> -19x + 2 = 0

=> -19x = -2

=> x = \(\frac{2}{19}\)

c) 2(5x - 8) - 3(4x - 5) = 4(3x - 4) + 11

=> 10x - 16 - 12x + 15 = 12x - 16 + 11

=> 10x - 16 - 12x + 15 - 12x + 16 - 11 = 0

=> (10x - 12x - 12x) + (-16 + 15 + 16 - 11) = 0

=> -14x + 4 = 0

=> -14x = -4

=> -7x = -2

=> x = 2/7

23 tháng 7 2020

lộn câu d nha sửa lại:

d) 2x(x2 − 2) + x2(1 - 2x) - x2

=> 2x3 − 4x + x2 − 2x3 − x2 = −12

=> -4x = 12 => x = -3

\(a,5\left(x^2-3x+1\right)+x\left(1-5x\right)=x-2\)

\(\Leftrightarrow5x^2-15x+5+x-5x^2-x+2=0\)

\(\Leftrightarrow-15x+7=0\)

\(\Leftrightarrow-15x=-7\)

\(\Leftrightarrow x=-\frac{7}{-15}\)

\(\Leftrightarrow x=\frac{7}{15}\)

17 tháng 5 2018

a, A= -3x+ 15x + 3x2 - 12x -3x + 10

    A= 15x - 15x + 10

    A= 10

b, B= 4x- 28x2 + 8x - 4x3 + 28x2 - 8x + 20

    B= 20

19 tháng 6 2019

\(b,x^3-3x^2-4x+12\)

\(\Leftrightarrow x^2\left(x-3\right)-4\left(x-3\right)\)

\(\Leftrightarrow\left(x-3\right)\left(x^2-4\right)\)

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

\(c,3x^3-7x^2+17x-5\)

\(\Leftrightarrow3x^3-x^2-6x^2+2x+15x-5\)

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

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

19 tháng 6 2019

\(\text{d) 2x}^4- 7x^3 - 2x^2 + 13x + 6\)
\(\text{= (2x^4 + 2x^3) - (9x^3 + 9x^2) + (7x^2 + 7x) + (6x + 6)}\)
\(\text{= 2x^3(x + 1) - 9x^2(x + 1) + 7x(x + 1) + 6(x + 1)}\)
\(\text{= (x + 1)(2x^3 - 9x^2 + 7x + 6)}\)
\(\text{= (x + 1)(2x + 1)(x - 3)(x - 2)}\)