Level:
Project ID:
1003261904
Accepted:
1
Clonable:
0
Easy:
0
Given the function
\[ f(x)=\sin x-3\cos x\text{ ,} \]
determine the set of all \( x \), \( x\in\mathbb{R} \), such that \( f''(x)+f(x)=0 \).
\( \mathbb{R} \)
\( \emptyset \)
\( \{k\pi;\ k\in\mathbb{Z}\} \)
\( \left\{(2k+1)\frac{\pi}2;\ k\in\mathbb{Z} \right\} \)