Yes it is a function because the four first 
coordinates 3,4,-3, and -4 are all different.

(Note: It doesn't matter that the second 
coordinates 2,5,5, and 2 are not all different. 
Only all the first coordinates must be different
in order for a relation to be a function)

The graph consists of these 4 points:

 

Notice that no point is directly above or
below any other point.  That is how you
can tell by looking at a graph whether
the relation is a function.  If any point
is directly above or below any other point,
then the relation is not a function.

Edwin