determine the domain on which the following function is decreasing.

Explanation:

Step1: Understand decreasing function

A function is decreasing when as $x$ increases, $y$ decreases.

Step2: Observe the graph

From the graph, we see that the function goes down - ward as $x$ moves from negative infinity to the vertex.

Step3: Locate the vertex

The vertex of the parabola is at $x=- 2$.

Answer:

$(-\infty,-2)$