Answer:
[tex]\left \{ {{y=x; \ \ x\le 0} \atop {y=4+ \frac12x;\ \ x>0}} \right.[/tex]
Step-by-step explanation:
If you look at the graph you see that:
before 0, the graph has same y as it has x, or y=x.
after 0, the graph starts at 4, and increases by 1 every 2 steps horizontally, or has a slope of 1/2.
Finally, the 0 has to be included in the blue part of the graph based on where the solid dot is.
