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- ta có : 7x - x = 6x suy ra 521 \(\div\) 519 + 3.2 -70 = 6x = 52 \(+\) 6 -1 = 25 +6-1 = 30 suy ra 6x = 30 v ậy x = 30 \(\div\) 6 = 5 =
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\(-7.\left(3x-5\right)+2.\left(7x-14\right)=28\)
\(\Leftrightarrow-21x+35+14x-28=28\)
\(\Leftrightarrow-7x+7=28\)
\(\Leftrightarrow-7x=21\)
\(\Leftrightarrow x=-3\)
Vậy \(x=-3\)
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\(-7\left(3x-5\right)+2\left(7x-14\right)=28\\ -21x+35+14x-28=28\\ -7x+7=28\\ -7x=21\\ x=-3\)
-7(3x - 5) + 2(7x - 14) = 28
-21x + 35 + 14x - 28 = 28
-7x = 28 - 35 + 28
-7x = 21
x = 21 : (-7)
x = -3
![](https://rs.olm.vn/images/avt/0.png?1311)
-7.(3x-5)+2.(7x-14)=28
-21x-35+14x-28=28
-21x+14x=28+35+28
-7x=94
x=94/-7
Vậy.................................
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a) 1/7 . 5/6 + 1/7 . 1/6 + -8/7
= 1/7 . ( 5/6 + 1/6 ) + -8/7
= 1/7 . 1 + -8/7
= 1/7 + -8/7 = -1
b) 3/5 . -4/9 . 5/3 . 18/7
= ( 3/5 . 5/3 ) . ( -4/9 . 18/7 )
= 1 . -8/7 = -8/7
c) 1/2 + -3/4 . 16/9
= 1/2 + -4/3 = -5/6
d) ( 1/7 + 5/14 ) . -28/3
= 1/2 . -28/3 = -14/3
![](https://rs.olm.vn/images/avt/0.png?1311)
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
Đúng 100%
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
![](https://rs.olm.vn/images/avt/0.png?1311)
\(a,3x-6=5x+2\)
\(3x-5x=2+6\)
\(-2x=8\)
\(x=-4\)
\(b,2\times\left(x-3\right)-3\times\left(x+7\right)=14\)
\(2x-6-3x-21=14\)
\(-x-27=14\)
\(x=-27-14\)
\(x=-41\)
a) 3x - 6 = 5x + 2
3x - 6 - 2 = 5x
3x - 8 = 5x
3x - 5x = 8
-2x = 8
x = -4
b) 2(x - 3) - 3(x + 7) = 14
2x - 6 - 3x - 21 = 14
(-x) - 27 = 14
(-x) = 41
x = -41
c) 3x2 - x - 2 = 0
x.(3x - 1) = 2
x.(3x - 1) = 2 = 1.2 = 2.1 = (-1).(-2) = (-2).(-1)
Xét 4 trường hợp ,ta có :
\(\left(1\right)\hept{\begin{cases}x=1\\3x-1=2\end{cases}\Rightarrow\hept{\begin{cases}x=1\\x=1\end{cases}}}\)(nhận)
\(\left(2\right)\hept{\begin{cases}x=2\\3x-1=1\end{cases}\Rightarrow\hept{\begin{cases}x=2\\x=\frac{2}{3}\end{cases}}}\)(loại)
\(\left(3\right)\hept{\begin{cases}x=-1\\3x-1=-2\end{cases}\Rightarrow\hept{\begin{cases}x=-1\\x=-\frac{1}{3}\end{cases}}}\)(loại)
\(\left(4\right)\hept{\begin{cases}x=-2\\3x-1=-1\end{cases}\Rightarrow\hept{\begin{cases}x=-2\\x=0\end{cases}}}\)(loại)
<=> -21x + 35 + 14x - 28 = 28
<=> -21x + 14x = 28 - 35 + 28
<=> -7x = 21
<=> x = 21 : (-7)
<=> x = -3
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