Question 91438
If on variable is constant, the line is either horizontal or vertical.  Take the following list of values (ordered pairs):

(-3,2) (-2,2) (-1,2) (0,2) (1,2) (2,2) (3,2)
Y values are the constant, therefore it is a horizontal line.
Y=2
{{{ graph( 300, 300, -5, 5, -5, 5, y=2 ) }}}