Please help me to solve this question.
closed as off-topic by Stanley Pawlukiewicz, MBaz, lennon310, A_A, Fat32 Jan 21 at 10:39
This question appears to be off-topic. The users who voted to close gave this specific reason:
- "This question appears to be homework. Complete answers to homework are off-topic, but specific questions about homework are acceptable if they include enough detail. Please edit the question to include more background about what you don't understand." – Stanley Pawlukiewicz, MBaz, lennon310, A_A, Fat32
When the spectrum is complex conjugate symmetric around $f_s/2$ (and multiples etc.) the corresponding signal is real valued and vice versa.
This holds for your example, meaning your signal should be real-valued. Your phase spectrum is interesting, since zero phase shift in all frequencies means your spectrum is real valued as well.