[tex]a) \\x^4=81=3^4\\
x=4\\b)\\
2^x\ \textless \ 31\ \textless \ 32=2^5\\
x\ \textless \ 5\\
x\in\{0,1,2,3,4\}\\
c)\\3^x\ \textless \ 242\ \textless \ 243=3^5\\
x\ \textless \ 5\\
x\in\{0,1,2,3,4\}\\
d) 2^x\ \textless \ 3^x|:2^x\\
(\frac{3}{2})^x\ \textgreater \ 1\\
1,5^x\ \textgreater \ 1\\
e)\\
3^x\ \textgreater \ 5^x|:5^x\\
(\frac{3}{5})^x\ \textgreater \ 1\\
0,6^x\ \textgreater \ 1\ imposibil \ in \ N
[/tex]