Bài 13:
a: 4x-2x=18
=>2x=18
hay x=9
b: \(3x+2x-15=40\)
=>5x=55
hay x=11
c: \(\left(x+1\right)+\left(x+4\right)+...+\left(x+28\right)=155\)
=>10x+145=155
=>10x=10
hay x=1
bài 4:
a) 541 + (218 - x) = 735
(218 - x) = 735 - 541
(218 - x) = 194
x = 218 - 194
x = 24
b) 96 - 3.(x + 1) = 42
3.(x + 1) = 96 - 42
3.(x + 1) = 54
x + 1 = 54 : 3
x + 1 = 18
x = 18 - 1
x = 17
c) 125 - 25.(x - 4) = 100
25.(x - 4) = 125 - 100
25.(x - 4) = 25
x - 4 = 25: 25
x - 4 = 1
x = 1 + 4
x = 5
d) 35 - (2x - 1) = 28
2x - 1 = 35 - 28
2x - 1 = 7
2x = 7 + 1
2x = 8
x = 8 : 2
x = 4
e) (x + 2) . 5 - 13 = 12
(x + 2) . 5 = 12 + 13
(x + 2) . 5 = 25
x + 2 = 25 : 5
x + 2 = 5
x = 5 - 2
x = 3
f) 96 - 3.(2x + 1) = 45
3.(2x + 1) = 96 - 45
3.(2x + 1) = 51
2x + 1 = 51 : 3
2x + 1 = 17
2x = 17 - 1
2x = 16
x = 16 : 2
x = 8
g) 580 : (3x - 25) = 329 -150 . 2
580 : (3x - 25) = 329 - 300
580 : (3x - 25) = 29
3x - 25 = 580 : 29
3x - 25 = 20
3x = 20 + 25
3x = 45
x = 45 : 3
x = 15
h) 312 - (2x + 5) = 217
2x + 5 = 312 - 217
2x + 5 = 95
2x = 95 - 5
2x = 90
x = 90 : 2
x = 45
i) 86 : (3x - 25) = 43
3x - 25 = 86 : 43
3x - 25 = 2
3x = 2 + 25
3x = 27
x = 27 : 3
x = 9
bài hơi nhiều nên mik chỉ làm 1 bài thôi bạn thông cảm
