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a) 17 - ( 2 + x ) = 3
2 + x = 17 - 3
2 + x = 14
x = 14 - 2
x = 12
Vậy x = 12
b)( 6+ x ) - ( 17 - 21 ) = -25
( 6 + x ) - ( - 4 ) = - 25
( 6+ x ) + 4 = - 25
6+ x = -25 - 4
6 + x =-29
x = -29 - 6
x = - 35
Vậy x = -35
c) -10 - ( 31 - x ) = 40
31- x = -10 - 40
31 - x = -50
x = 31 - ( - 50 )
x = 81
Vậy x = 81
d ) / x - 7 / + 13 = 25
/ x - 7 / = 25 - 13
/ x - 7 / = 12
\(\orbr{\begin{cases}x-7=12\\x-7=-12\end{cases}}\Rightarrow\orbr{\begin{cases}x=12+7\\x=-12+7\end{cases}}\Rightarrow\orbr{\begin{cases}x=19\\x=-5\end{cases}}\)
Vậy x = 19 hoac x =-5
A) 17 - (2 + x) = 3
2 + x = 17 - 3
2 + x =14
x = 14 - 2
x = 12
B) (6 + x) - (17 - 21) = -25
(6 + x) - (-4) = -25
6 + x = -25 + (-4)
6 + x = -29
x = -29 - 6
x = -35
C) -10 - (31 - x) = 40
31 - x = -10 - 40
31 - x = -50
x = 31 - (-50)
x = 81
D) | x - 7| + 13 = 25
|x - 7| = 25 - 13
|x - 7| = 12
x = 12 + 7
x = 19
k cho tớ nha bn
a) \(-x+821+534=499+\left(x-84\right)\)
\(-x-x=499-84-821-534\)
\(-2x=-940\)
\(x=470\)
b) \(x-96=\left(448-x\right)-150\)
\(x+x=448-150+96\)
\(2x=394\)
\(x=197\)
c) \(-\left(754+x\right)=\left(x-12-741\right)-23\)
\(-754-x=x-12-741-23\)
\(-x+x=-12-741-23+754\)
\(0x=2\)
\(x\)ko tồn tại
d) \(\left(6+x\right)-\left(17-21\right)=-25\)
\(6+x-17+21=-25\)
\(x=-25-6+17-21\)
\(x=-35\)
e) \(17-\left(x+2\right)=3\)
\(17-x-2=3\)
\(-x=3-17+2\)
\(-x=-12\)
\(x=12\)
h) \(-10-\left(31-x\right)=40\)
\(-10-31+x=40\)
\(x=40+10+31\)
\(x=81\)
k mk nha bạn 
1a) 25 .8 - 12.5 + 272 :17 - 8
= 200 - 60 + 16 - 8
= 140+16-8
= 156 - 8
= 148
b) 125: 25 +14 - 142 : 71
= 5 + 14 - 2
= 19 - 2 = 17
c) 13. 17 - 256: 16 + 14 : 7 - 1
= 221 - 16 + 2 - 1
= 205 + 2 - 1
= 207 - 1 = 206
d) 15 . 24 - 14 . 5 (145 : 5 - 27)
= 360 - 70 (29- 27)
= 360 - 70 . 2
= 360 - 140
= 220
2a) 37 + x = 55
x= 55 - 37
x = 18
b) x- 31 = 24
x = 24 + 31
x = 55
c) 21 (x-11) = 21
x - 11 = 21 : 21
x = 1 +11
x = 12
d ) 9. (x - 29)= 0
x - 29 = 0 :9
x = 29
e) (x - 1954) . 5 = 50
x - 1954 = 50 : 5
x = 1964
f ) 30 . 60 - x = 30
1800 - x = 30
x = 1800 - 30
x = 1770
Viết mỏi tay quá huhuh
Bài 1: Tìm x biết
a) x - 50 : 25 = 8
x- 2 = 8
x= 8+2
x=10
b) (x + 40).15 = 75.24
x+40 = 75.24:15
x+40 = 70
x= 30
c) (x - 32) - 15 = 0
x- 31 = 15
x= 15+ 31
x = 46
d) 1234 : x = 2
x= 1234:2
x = 617
e) (x - 34).26 = 0
x- 34 = 0: 26
x= 0 + 34
x= 34
f) 152 + (x + 231) : 2 = 358
(x+231):2 = 358- 152
(x+231):2 = 206
x+ 231 = 206*2
x= 412 - 231
x= 181
1.
a) x - 50 : 25 = 8
x - 2 = 8
x = 10
b) (x + 40) . 15 = 75 . 24
x + 40 = 75 . 24 : 15
x + 40 = 120
x = 80
c) (x - 32) - 15 = 0
x - 32 = 15
x = 47
d) 1234 : x = 2
x = 617
e) (x - 34) . 26 = 0
Thỏa mãn điều kiện x - 34 = 0
x = 34
f) 152 + (x + 231) : 2 = 358
(x + 231) : 2 = 206
x + 231 = 412
x = 181
2.
a) 45 . (2 . x - 4) . 13 = 0
Thỏa mãn điều kiện 2 . x - 4 = 0
x = 2
b) 5 . x - 38 : 19 = 13
5 . x - 2 = 13
5 . x = 15
x = 3
c) 100 - 3 . (8 + x) = 1
3 . (8 + x) = 99
8 + x = 33
x = 25
d) [(x + 12) - 17] : 5 = 4
(x + 12) - 17 = 20
x + 12 = 37
x = 25
e) 84 - 4 . (2 . x + 1) = 48
4 . (2 . x + 1) = 36
2 . x + 1 = 9
2 . x = 8
x = 4
a) \(-x+821+534=499+\left(x-84\right)\)
\(\Leftrightarrow-x+821+534=499+x-84\)
\(\Leftrightarrow821+534-499+84=x+x\)
\(\Leftrightarrow940=2x\)
\(\Leftrightarrow x=\dfrac{940}{2}\)
\(\Leftrightarrow x=470\)
Vậy \(x=470\)
b) \(x-96=\left(448-x\right)-150\)
\(\Leftrightarrow x-96=448-x-150\)
\(\Leftrightarrow x+x=96+448-150\)
\(\Leftrightarrow2x=394\)
\(\Leftrightarrow x=\dfrac{394}{2}\)
\(\Leftrightarrow x=197\)
Vậy \(x=197\)
c) \(- (754 + x) = (x - 12 - 741) - 23\)
\(\Leftrightarrow-754-x=x-12-741-23\)
\(\Leftrightarrow-754+12+741+23=x+x\)
\(\Leftrightarrow22=2x\)
\(\Leftrightarrow x=\dfrac{22}{2}\)
\(\Leftrightarrow x=11\)
Vậy \(x=11\)
d) \((6 + x) - (17 - 21) = -25\)
\(\Leftrightarrow6+x-17+21=-25\)
\(\Leftrightarrow x=-25-6+17-21\)
\(\Leftrightarrow x=-35\)
Vậy \(x=-35\)
e) \(17-\left(x+2\right)=3\)
\(\Leftrightarrow17-x-2=3\)
\(\Leftrightarrow17-2-3=x\)
\(\Leftrightarrow x=12\)
Vậy \(x=12\)
h) \(-10 - (31 - x) = 40\)
\(\Leftrightarrow-10-31+x=40\)
\(\Leftrightarrow x=40+10+31\)
\(\Leftrightarrow x=81\)
Vậy \(x=81\)
Bài toán 1 : Tìm x nguyên biết.
a. 3 ≤ x – 2 < 5
=>3-2 < x-2 < 5-2
=>1 < x < 3
=>x=1
Vậy x=1
b. 0 ≤ x – 5 ≤ 2
=>0-5 < x-5 < 2-5
=>-5 < x < -3
=>x=-4
Vậy x=-4
Bài toán 2 : Tính hợp lý.
a. 4567 + (1234 – 4567) -4
=4567+1234-4567-4
=(4567-4567)+(1234-4)
=0+1230
=1230
b. 2001 – (53 + 1579) – (-53)
=2001-53-1579+53
=(2001-1579)+(-53+53)
=422+0
=422
c. 35 – 17 + 2017 – 35 + (-2017)
=(35-35)+[2017+(-2017)]-17-35
=0+0-17-35
=0-17-35
=-52
d. 37 + (-17) – 37 + 77
=(37-37)+[-17+77]
=0+60
=60
e. –(-219) + (-219) – 401 + 12
=0-401+12
=-389
f. |-85| – (-3).15
=85+3.15
=85+45
=130
g. 11.107 + 11.18 – 25.11
=11.(107+18-25)
=11.100
=1100
h. 115 – (-85) + 53 – (-500 + 53)
=115+85+53+500-53
=(53-53)+(115+85+500)
=0+700
=700
k. (-18) + (-31) + 98 + |-18| + (-69)
=-18-31+98+18-69
=(-18+18)+(-31-69)+98
=0+(-100)+98
=-100+98
=-2
Bài toán 4 : Tìm x, biêt.
a. 5x – 16 = 40 + x
5x - x = 40 + 16
4x = 56
x = 56 : 4
x=14
b. 4x – 10 = 15 – x
4x + x = 15 + 10
5x = 25
x = 25 : 5
x = 5
c. -12 + x = 5x – 20
-12 + 20 = 5x - x
8 = 4x
x = 8 : 4
x = 2
d. 7x – 4 = 20 + 3x
7x - 3x = 20 + 4
4x=24
x=24:4
x=6
e. 5x – 7 = – 21 – 2x
5x + 2x = -21+7
7x = -14
x = -14 : 7
x = -2
f. x + 15 = 7 – 6x
x + 6x = 7 - 15
7x = -8
x = -8/7
g. 17 – x = 7 – 6x
17 - 7 = -6x + x
10 = -7x
x=10/-7
h. 3x + (-21) = 12 – 8x
3x + 8x = 12 + 21
11x = 33
x = 33:11
x=3
k. 125 : (3x – 13) = 25
3x-13=125:25
3x-13=5
3x=5+13
3x=18
x=18:3
x=6
l. 541 + (218 – x) = 735
218-x=735-541
218-x=693
x=218-693
x=-475