a) (x-5)3 = ( x - 5)2
=>\(\left\{{}\begin{matrix}x-5=0\\x-5=1\end{matrix}\right.\) =>\(\left\{{}\begin{matrix}x=5\\x=6\end{matrix}\right.\)
vậy x=5 hoặc x=6
b) 22x+1 - 1 = 31
=> 22x+1=31+1
=> 22x+1=32
=> 22x+1=25
=> 2x+1=5
=> 2x=6
=> x=3
vậy x=3
c) (x - 5)4 - 3 = 78
=> (x-5)4=81
=> (x-5)4=34
=> x-5=3
=> x=8
vậy x=8