Giải thích các bước giải:
`e)`
`(3x+1)^2-2020^0=3.2^4`
`=>(3x+1)^2-1=3.16`
`=>(3x+1)^2-1=48`
`=>(3x+1)^2=48+1`
`=>(3x+1)^2=49`
`=>(3x+1)^2=(+-7)^2`
`=>[(3x+1=7),(3x+1=-7):}`
`=>[(3x=7-1),(3x=-7-1):}`
`=>[(3x=6),(3x=-8):}`
`=>[(x=6:3),(x=-8/3):}`
`=>[(x=2),(x=-8/3):}`
Vậy `x\in{2;-8/3}`
`f)`
`3^x+3^(x+3)=252`
`=>3^x+3^x .3^3=252`
`=>3^x + 3^x . 27=252`
`=>3^x .(1+27)=252`
`=>3^x . 28=252`
`=>3^x=252:28`
`=>3^x=9`
`=>3^x=3^2`
`=>x=2`
Vậy `x=2`
