Asymptotic notation in equations

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I've been working my way through Introduction to Algorithms, Fourth Edition and am having a hard time with one of the exercises in chapter 3, which is mostly about standard notation.

The exercise is as follows:

3.3-3

Use equation (3.14) or other means to show that $(n + o(n))^k = Θ(n^k)$ for any real constant $k$. Conclude that $⌈n⌉^k = Θ(n^k)$ and $⌊n⌋^k = Θ(n^k)$.

Equation (3.14) is as follows:

$1 + x ≤ e^x$

I was unable to make a connection between this equation and the exercise, but reasoning about the properties of the notation, I think that when $n$ is sufficiently large, the $o(n)$ in $n + o(n)$ is relatively insignificant compared to $n$, and so the part inside the brackets is just $n^k$, which is a member of $Θ(n^k)$.

For $⌈n⌉^k$ and $⌊n⌋^k$ I'm really not sure what the exercise wants me to think about, because any $n^k$ is $Θ(n^k)$.

I would really appreciate a hint as to how I could repeat the exercise as intended, using equation (3.14), along with any other comments about the above.