The graph has 3 parts
The decreasing part that slopes downwards, the increasing part that slopes upwards and the constant part that ends it as a straight line.
The decreasing part is that on the left side that begins from minus infinity on the negative x-axis and ends exactly at the origin before picking up.
Therefore, the interval of the graph decreasing starts from minus infinity to 0
[tex](-\infty,0)[/tex]
