Final answer:
The set W of all nonnegative functions in C(-∞, ∞) is not a subspace of the vector space because it is not closed under scalar multiplication (Option 4).
Step-by-step explanation:
The question is whether the set W, consisting of all nonnegative functions in C(-∞, ∞), is a subspace of the vector space. To determine whether W is a subspace, it must satisfy three conditions:
- The zero vector must be in W.
- W must be closed under vector addition.
- W must be closed under scalar multiplication.
The set W fails to be a subspace because it is not closed under scalar multiplication. If we multiply a nonnegative function by a negative scalar, the result is not a nonnegative function, hence it is not in W.
Therefore, the correct choice would be No, because W is not closed under scalar multiplication, which corresponds to Option 4.