Question

 

 

tìm số tự nhiên x để:3^x+2+3^x+1+3^x<1053

Answer 1

\(3^{x+2}+3^{x+1}+3^x< 1053\)

\(3^x\left(3^2+3+1\right)< 1053\)

\(3^x.13< 1053\)

\(3^x< 81\)

\(3^x< 3^4\)

\(x< 4\)

Mà x là stn 

\(\Rightarrow x\in\left\{0;1;2;3\right\}\)

Answer 2

\(3^{x+2}+3^{x+1}+3^x< 1053\)

\(\Leftrightarrow13.3^x< 1053\)

\(\Leftrightarrow3^x< 1053:13\)

\(\Leftrightarrow3^x< 81\)

\(\Leftrightarrow3^x< 3^4\)

<=> x < 4

\(\Rightarrow x\in\left\{0;1;2;3\right\}\)