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!!!}`
