Answer
$$\theta=55^o.$$
Work Step by Step
Since $ n_1=\langle 3,-5,2\rangle $ and $ n_2=\langle 1,0,1\rangle $, then we have
\begin{align*}
\cos \theta &=\frac{n_1 \cdot n_2}{\|n_1\|\|n_2\|}\\
&=\frac{3+0+2}{\sqrt{9+25+4}\sqrt{1+0+1}}\\
&=\frac{5}{\sqrt{38}\sqrt{2}}.
\end{align*}
Taking the inverse cosine of the above, we get:$$\theta=55^o.$$
