Question 1129677
{{{y=-9}}} is horizontal line

Horizontal lines have a slope of {{{0}}}. Thus, in the slope-intercept equation
 
{{{y = mx + b}}}, and if  {{{m = 0}}} the equation becomes {{{y = b}}}, where {{{b}}} is the y-coordinate of the y-intercept 

and graph looks like this:

 {{{ graph(600, 600, -15, 15, -15, 15, -9,-9) }}}