a) \(3^{-2}\cdot9^n=3^n\)
\(\Rightarrow3^{-2}\cdot3^{2n}=3^n\)
\(\Rightarrow3^{2n-2}=3^n\Rightarrow2n-2=n\)
\(\Rightarrow2n-n=2\)
=> n = 2
Vậy n = 2
b) \(\left(\dfrac{9}{25}\right)^n=\left(\dfrac{3}{5}\right)^{-4}\)
=> \(\left(\dfrac{3}{5}\right)^{2n}=\left(\dfrac{3}{5}\right)^{-4}\)
=> 2n = -4
=> n = -2
Vậy n = -2