\(3^{x+2}+3^{x+1}+3^x< 1053\)
\(3^x\left(3^2+3+1\right)< 1053\)
\(3^x.13< 1053\)
\(3^x< 81\)
\(3^x< 3^4\)
\(x< 4\)
Mà x là stn
\(\Rightarrow x\in\left\{0;1;2;3\right\}\)
\(3^{x+2}+3^{x+1}+3^x< 1053\)
\(\Leftrightarrow13.3^x< 1053\)
\(\Leftrightarrow3^x< 1053:13\)
\(\Leftrightarrow3^x< 81\)
\(\Leftrightarrow3^x< 3^4\)
<=> x < 4
\(\Rightarrow x\in\left\{0;1;2;3\right\}\)