[tex]\displaystyle \\
a)~~\text{Daca doua puteri egale cu baze diferite si exponenti egali, atunci} \\
\text{exponentii sunt egali cu zero.} \\
3^n=7^n ~~\Longrightarrow~~\boxed{n=0} \\ \\
b) \\ 2^n=4^3\\
2^n =(2^2)^3 \\
2^n =2^{2\times3} \\
2^n =2^6 ~~\Longrightarrow~~\boxed{n=6}
[/tex]
[tex]c) \\
3^{2n} \ \textless \ 9^3 \\
3^{2n} \ \textless \ (3^2)^3 \\
3^{2n} \ \textless \ 3^{2\times 3} \\
3^{2n} \ \textless \ 3^6 \\
2n \ \textless \ 6 ~~| : 2 \\
n \ \textless \ 3 ~~\Longrightarrow~~\boxed{n \in \{0;~1;~2\} } \\ \\
d)
7^n=1 ~~\Longrightarrow~~\boxed{n=0}[/tex]