`a`) `2.(x-1)^3=2^4`
`2.(x-1)^3=16`
`(x-1)^3=16:2`
`(x-1)^3=8`
`text{Vì}` `8=2^3`
`=>` `(x-1)^3=2^3`
`=>` `x-1=2`
`=>` `x=2+1`
`=>` `x=3`
`b`) `(2x+1)^2 :3=27`
`(2x+1)^2=27:3`
`(2x+1)^2=9`
`text{ Vì}` `9=3^2`
`=>` `(2x+1)^2=3^2`
`=>` `2x+1=3`
`=>` `2x=3-1`
`=>` `2x=2`
`=>` `x=2:2`
`=>` `x=1`