Could someone explain to me how to find the limits for the following two expressions as n approaches infinity:

a)$\displaystyle

\frac{{5^{n + 2} - 7^{n + 2} }}{{5^n - 7^n }}

$

b)$\displaystyle

\frac{{n + ( - 2)^n }}{{n - ( - 2)^n }}

$

help is hugely appreciated.