Range and Domain of a function
Domain
Having the graph of a function we want to find its domain, this means that we want to find the x-values that the function "covers". We are going to draw a shadow to the x-axis in order to find those values:
We see that the x-values the function takes go from -1 to 4. Since the line of the function is an open circle the it doesn't pass over x = -1 and x = 4. Then
Domain = (-1, 4)
Range
We want to find y-values the function "covers" in order to find its range. Similarly, we draw a shadow, but it might be a leaned shadow: