Here is how you can do this: Replace the inequality with an equality, i.e. write -2x+y=10. This is a line equation, so you graph the line: y = 2x + 10. The line divides the entire plane into two halves. The question then is which half corresponds to the inequality.Originally Posted by Nicv
To decide, set x = y = 0 : You notice that you obtain a correct inequality. Thus the point (0,0) is in the half plane that is described by the inequality, i.e. all points below the line are described by the inequality.