I can't figure out how to solve this:
= ?
Please help!
You don't need to apply that Rule, just remember that
$\displaystyle \forall\,x\in\mathbb R,\,\lim_{n\to\infty}\left(1+\frac xn\right)^n=e^{x}.$
And,
$\displaystyle \lim_{x \to \infty } \left( {1 + \frac{7}
{x}} \right)^{x/5} = \lim_{x \to \infty } \left[ {\left( {1 + \frac{7}
{x}} \right)^x } \right]^{1/5}$