\[\frac{5^{n} + 1}{5^{- n} + 1} = \frac{5^{n} + 1\ }{\frac{1}{5^{n}} + 1} = \frac{5^{n} + 1}{\frac{1 + 5^{n}}{5^{n}}} =\]
\[= \frac{(5^{n} + 1) \cdot 5^{n}}{5^{n} + 1} = 5^{n}\]