To draw the graph of a linear equation , two points are more than enough to draw a line.
But sometimes we may commit a mistake and then if we draw the line, everything appears good. As two points shall always define a line irrespective of the points are correct or not.
So in order to make sure that the points we obtained are correct , we take a third point to ensure that the two points calculated earlier are correct and all points lie on the same line. If they don't we have committed some mistake.
