Bài 1: 

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

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

\(\Rightarrow16x-5=x-2\)

\(\Rightarrow16x-x=5-2\)

\(\Rightarrow15x=3\)

\(\Rightarrow x=\dfrac{15}{3}=5\)

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

\(\Rightarrow12x^2-12x^2-20x=10x-17\)

\(\Rightarrow-20x=10x-17\)

\(\Rightarrow-20x-10x=-17\)

\(\Rightarrow-30x=-17\)

\(\Rightarrow x=\dfrac{-30}{-17}=\dfrac{30}{17}\)

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

\(\Rightarrow-4x^2+20x+7x^2-28x-3x^2=12\)

\(\Rightarrow-8x=12\)

\(\Rightarrow x=\dfrac{12}{-8}=-\dfrac{4}{3}\)

Bài 2: 

a) \(\left(x+5\right)\left(x-7\right)-7x\left(x-3\right)\)

\(=x^2-7x+5x-35-7x^2+21x\)

\(=-6x^2+19x-35\)

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

\(=x^3-x^2-2x-x^2+x-5x-5\)

\(=x^3-2x^2-6x-5\)

c) \(\left(x-5\right)\left(x-7\right)-\left(x+4\right)\left(x-3\right)\)

\(=x^2-7x-5x+35-x^2-3x+4x-12\)

\(=11x+23\)

d) \(\left(x-1\right)\left(x-2\right)-\left(x+5\right)\left(x+2\right)\)

\(=x^2-2x-x+2-x^2+2x+5x+10\)

\(=4x+12\)

a) -5 . (2 - x) + 4(x - 3) = 10x - 15

-10 + 5x + 4x -12 = 10x - 15

5x + 4x - 10x = -15 + 10 + 12

-x = 7

x = -7

b) 5 . (3 - 2x) + 5 . (x - 4) = 6 - 4x

15 - 10x + 5x - 20 = 6 - 4x

-10x + 5x + 4x = 6 - 15 + 20

-x = 11

x = -11

c) - 7 . (3x - 5) + 2 . (7x - 14) = 28

-21x + 35 + 14x - 28 = 28

-21x + 14x = 28 - 35 + 28

-7x = 21

x = 21 : (-7)

x = -3

d) 4 . (x - 5) - 3 . (x + 7) = 5 . (-4)

4x - 20 - 3x - 21 = -20

4x - 3x = -20 + 20 + 21

x = 21

e) 5 . (4 - x) - 7. (-x + 2) = 4 - 9 + 3

20 - 5x + 7x - 14 = -2

-5x + 7x = -2 - 20 + 14

2x = -8

x = -8 : 2

x = -4

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câu c

- 7 ( 3x - 5 ) + 2 ( 7x - 14 ) = 28

- 21x + 35 + 14x - 28 = 28

 21x - 14x = 35 - 28 - 28

7x = - 21

x = ( - 21) : 7

x = - 3 

a, -5 .(2- x) +4 (x-3) =10x -15
<=> -19 +5x +4x-12 -10x +15=0
<=> -x=16
<=>x=16
b, 5(3-2x) +5.(x-4)=6-4x
<=> 15-10x +5x-20 -6+4x=0
<=> -x=-11
<=> x=11
c, -7.(3x-5) +7.(7x -14)=28
<=> -21x +35+49x -98-28=0
<=>28x=-91
<=>x= -\(\frac{13}{4}\)
d, 4.(x-5) -3.(x+7)=5.(-4)
<=>4x-20-3x-21=-20
<=>x=21
e,5.(4-x)-7.(-x+2)=4-9+3
<=>20x -5x +7x -14= -2
<=>22x=12
<=>x=\(\frac{6}{11}\)
P tự kết luận nhé k hiểu hay mk sai chỗ nào p pảo mk nhé

1/   Suy ra: -35 + 7x - 2x + 20 = 15

                5x - 15 = 15

                 5x = 30

                  x = 6

2/  Suy ra:  4x - 20 - 3x - 21 = -19

                   x - 41  = -19

                    x  = 22

3/   Suy ra:   8 - 4x + 3x - 15 = 14

                    -7 -x = 14

                      x = -7 -14

                      x = -21

4/    Suy ra:   7x - 63 - 30 + 5x = -6 + 11x

                      7x + 5x - 11x = -6 +63 + 30

                       x   =    87

5/    Suy ra:  -21x +35 + 14x - 28 = 28

                       -21x + 14x = 28 +28 - 35

                         -7x = 21

                             x= -3

6/     Suy ra:  20 - 5x + 7x - 14 = -2

                        2x   =   -8

                          x = -4

7/    Suy ra:   4x +15 -5x = 7

                      -x = -8

                        x = 8

 8/   Suy ra:   5x - 35 +30 -10x = 20

                      -5x - 5 = 20

                          -5x = 25

                            x = -5

9/    Suy ra:     35 - 7x + 5x - 10 = 15

                         -7x + 5x = 15 +10 - 35

                        -2x = -10

                          x = 5

1: \(\dfrac{4}{23}+\dfrac{5}{21}+\dfrac{1}{2}-\dfrac{4}{23}+\dfrac{16}{21}\)

\(=1+\dfrac{1}{2}\)

\(=\dfrac{3}{2}\)

2: \(\left(\dfrac{1}{3}+\dfrac{12}{67}+\dfrac{13}{41}\right)-\left(\dfrac{79}{67}-\dfrac{28}{41}\right)\)

\(=\dfrac{1}{3}+\dfrac{12}{67}+\dfrac{13}{41}-\dfrac{79}{67}+\dfrac{28}{41}\)

\(=\dfrac{1}{3}\)

a: (3x-2)(4x+5)=0

=>3x-2=0 hoặc 4x+5=0

=>x=2/3 hoặc x=-5/4

b: (2,3x-6,9)(0,1x+2)=0

=>2,3x-6,9=0 hoặc 0,1x+2=0

=>x=3 hoặc x=-20

c: =>(x-3)(2x+5)=0

=>x-3=0 hoặc 2x+5=0

=>x=3 hoặc x=-5/2

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