x + 2y + 6 = 0
Subtract (x + 6) from each side :
2y = -x - 6
Divide each side by 2 :
y = -1/2 x - 3
When the equation is in this form, you can look at it and know immediately
that the slope of its graph is -1/2 and its graph crosses the y-axis at y= -3.
In order to graph it, draw a straight line with a slope of -1/2 through the point
on the y-axis where y= -3 .