Question 243498
The slope of a line is the change in y divided by the change in x.  If the slope = 0, then there is no change in y, regardless of the change in x.  So we have a straight horizontal line.
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You have been given the point (0,-1) as being on the line, so that means the horizontal line runs across the graph at y=-1.  That's the formula.  Here's the graph.
{{{
graph(500,500,-10,10,-10,10,-1)
}}}