Problem 734 (difficulty: 2/10)

Let \(\displaystyle f(x)=C_1 \cos x+ C_2\sin x\). \(\displaystyle f''(x)+f(x)=?\)

Give me another random problem!

Subject, section:
Requested difficulty:
Request for a concrete problem:I want problem no.

Supported by the Higher Education Restructuring Fund allocated to ELTE by the Hungarian Government