Answer:
(-∞, 0].
Explanation:
This set states that any value of x will always be less or equal to 0, therefore, x moves from -∞ to 0, including the 0. This, in interval notation is:
(-∞, 0].
Note that we use parenthesis for the side of -∞ and a square bracket for the 0, this is because both -∞ and ∞ are always categorized as "not contained" in a group of numbers. On the other hand, we write 0 with a square bracket next to it because this group of numbers contains the 0, because x can be less or equal to 0.