Answer:
Range [-2,2]
Cosine value varies from -1 to 1, hence -2cos 3x can vary from +2 to -2. The range of the given function , in interval notation, would thus be [-2,2]. In set builder notation it can be expressed as
{y∈R∣−2≤y≤2 }
It most likely might be wrong though so sorry for that.
