Ta có: \(3^x+3^{x+1}+3^{x+2}=351\)
\(\Leftrightarrow3^x+3^x\cdot3+3^x\cdot9=351\)
\(\Leftrightarrow3^x\left(1+3+9\right)=351\)
\(\Leftrightarrow3^x=\frac{351}{13}=27\)
\(\Leftrightarrow3^x=3^3\)
hay x=3
Vậy: x=3
3^x + 3^x+1 + 3^x+2 = 351
=> 3^x + 3^x * 3 + 3^x * 9 = 351
=> 3^x * (1+3+9) = 315
=> 3^x * 12 = 315
=> 3^x = 315 / 12 = 26,25
=> x = 2.97