a) `(2x-1)^2 - 5 = 20`
`=> (2x-1)^2 = 25`
+) `(2x-1)^2 = 5^2`
`=> 2x-1=5`
`=> 2x=6`
`=> x=3`
+) `(2x-1)^2 = (-5)^2`
`=> 2x-1 =-5`
`=> 2x = -4`
`=> x= -2`
Vậy `x=3` hoặc `x=-2`
3) `(x-7)^(x+1) - (x-7)^(x+11)=0`
`=> (x-7)^(x+1) - (x-7)^(x+1+10) =0`
`=> (x-7)^(x+1) -(x-7)^(x+1) . (x-7)^10 =0`
`=> (x-7)^(x+1) [ 1 - (x-7)^10]=0`
+) `(x-7)^(x+1)=0`
`=> x-7=0`
`=> x=0+7`
`=>x=7`
+) `1 -(x-7)^10 =0`
`=> (x-7)^10 =1`
`=>` \(\left[ \begin{array}{l}x-7=1\\x-7= -1\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=8\\x=6\end{array} \right.\)
Vậy `x=7` hoặc `x=8` hoặc `x=6`
