Observe the graph:

The left portion of the graph is the constant function .

There is a closed dot at , so the domain for this part of the function is .

The center portion of the graph is the line .

There are open circle at and ,so the domain for this part is .

The right portion of the graph is the constant function .

There is a closed dot at , so the constant function is defined for .

Therefore the function is .

The function is .