Which could be the entire interval over which the function, f(x), is positive?
(—,1 )
(-2,1 )
(—,0)
(1, 4 )

Just look at the positive coordinates, so in this case:

(1,4)

sample answer: you can determine whether each element of the domain is paired with exactly one element of the range. for example, if given a graph, you could use the vertical line test; if a vertical line intersects the graph more than once, then the relation that the graph represents is not a function.