a)
\(\left(2x-1\right)^2-81=0\)
\(\Rightarrow\left(2x-1\right)^2=9\)
\(\Rightarrow\left[\begin{array}{nghiempt}2x-1=9\\2x-1=-9\end{array}\right.\)
\(\Rightarrow\left[\begin{array}{nghiempt}x=5\\x=-4\end{array}\right.\)
Vậy x=5 ; x = - 5
b)
\(3^{x+2}+3^{x+1}-3^x=297\)
\(\Rightarrow3^x\left(9+3-1\right)=297\)
\(\Rightarrow3^x.11=297\)
\(\Rightarrow3^x=27\)
=> x = 3
Vậy x = 3
c)
\(3^x+2.3^{x-1}=405\)
\(\Rightarrow3^{x-1}\left(3+2\right)=405\)
\(\Rightarrow3^{x-1}.5=405\)
\(\Rightarrow3^{x-1}=81\)
=> x - 1 = 4
=> x = 5
Vậy x = 5
a) ( 2x-1 ) 2 - 81 = 0
( 2x-1 ) 2 = 0 + 81
( 2x-1 ) 2 = 81
( 2x-1 ) 2 = 92
2x-1 = 9
2x= 9+1
2x = 10
x= 10:2
x=5
Vậy x=5.
