a)  123-5.(x+4)= 38                                                       

5.(x+4)= 123-38

5.(x+4)= 85

x-4=85:5

x-4= 17

x=17+4

⇒ x=  21  . vậy x = 21

b)10+2x= 2.( 3²-1)

10+2x= 16

2x= 16-10

2x=6

x= 6: 2

x= 3. vậy x= 3

c) 2x-138= 2³.3²

2x-138= 72

2x= 72+138

2x= 210

x=210:2

x= vậy x =105

d) [102+( 28-2x)]:20-5=1 

[102+( 28-2x)]:20= 1+5

[102+( 28-2x)]:20=6 

[102+( 28-2x)]= 6.20

102+( 28-2x)= 120

28-2x= 120-102

28-2x= 18

2x=28-18

2x=10

x= 10:2

x=5. vậy x=5 

e) 231- ( x-6 )= 1339:13

231- ( x-6 )= 103

x-6=231-103

x-6=128

x=128+6

x=134. vậy x= 134

f) 3|x| = 5²-1

3|x|= 24

x= 24:3

x=8. vậy x= 8

g) |x-1|= 3

x-1=3

x= 3+1

x=4. vậy x=4

h) 3x-121= 2³.3²+2

3x-121=8.9+2

3x-121=74

3x= 74+121

3x= 195

x= 195:3

x= 65. vậy x= 65

Giải thích:

`\text{A,  123-5.(x+4)= 38 }`

 `\text{5.(x+4)= 123-38}`

`\text{5.(x+4)= 85}`

`\text{x-4=85:5}`

`\text{x-4= 17}`

`\text{x=17+4}`

`\text{⇒ x=  21}`

    `\text{Vậy x = 21}`

`\text{B,}``10+2x= 2.( 3^2-1)`

`\text{10+2x= 16}`

`\text{2x= 16-10}`

`\text{2x=6}`

`\text{x= 6: 2}`

`\text{x= 3}`

`\text{Vậy x= 3}`

`\text{C,}` `2x-138= 2^3 . 3^2`

`\text{2x-138= 72}`

`\text{2x= 72+138}`

`\text{2x= 210}`

`\text{x=210:2}`

`\text{x= 105}`

`\text{Vậy x =105}`

`\text{D, [102+( 28-2x)]:20-5=1}`

`\text{[102+( 28-2x)]:20= 1+5}`

`\text{[102+( 28-2x)]:20=6 }`

`\text{[102+( 28-2x)]= 6.20}`

`\text{102+( 28-2x)= 120}`

`\text{28-2x= 120-102}`

`\text{28-2x= 18}`

`\text{2x=28-18}`

`\text{2x=10}`

`\text{x= 10:2}`

`\text{x=5}`

`\text{Vậy x=5 }`

`\text{E, 231- ( x-6 )= 1339:13}`

`\text{231- ( x-6 )= 103}`

`\text{x-6=231-103}`

`\text{x-6=128}`

`\text{x=128+6}`

`\text{x=134}`

`\text{Vậy x= 134}`

`\text{F,}` `3|x| = 5^2-1`

`\text{3|x|= 24}`

`\text{x= 24:3}`

`\text{x=8}`

`\text{Vậy x= 8}`

`\text{G, |x-1|= 3}`

`\text{x-1=3}`

`\text{x= 3+1}`

`\text{x=4.}`

`\text{Vậy x=4}`

`\text{H,}` `3x-121=` `2^3`.`3^2+2`

`\text{3x-121=8.9+2}`

`\text{3x-121=74}`

`\text{3x= 74+121}`

`\text{3x= 195}`

`\text{x= 195:3}`

`\text{x= 65}`

`\text{Vậy x= 65.}`

`\text{Học tốt!!!}`