Question 57627
This is a special case, When you have y=k, where k is a real number and there's no x.  Then you have a horizontal line going through k.
y + 1 = 0
y+1-1=0-1
y=-1
You have a horizontal line going through -1, like this:
{{{graph(300,200,-10,10,-10,10,-1)}}}
Happy Calculating!!!