5.3x=405
3x=405:5
3x=81
3x=34
Vậy x=4
2x:8=4
2x=4.8
2x=32
2x=25
Vậy x=5
x28=x5
x^28-x^5=0
x^5.x^23-x^5.1=0
x^5.(x^23-1)=0
suy ra x^5=0 hoặc x^23-1=0 suy ra x^5=0^5 hoặc x^23=0+1=1 suy ra x=0 hoặc x^23=1^23 suy ra x=0 hoăc x=1
9
(x-2)^4=256
(x-2)^4=4^4
x-2=4
x=4+2=6
(x+1)^3=125
(x+1)^3=5^3
x+1=5
x=5-1=4