Travel to learn happy go lucky, indifferent point, walk to stop. Don't be afraid to miss anything, because on the road you have harvested freely in a good mood.

Time flies, quiet and indifferent, this is nature's hand, in the years of the passage of time on both sides of the passing of people, from the bright point of the point from warmth.

We discuss two important properties of indifferent curves, point out the equivalence of them and obtain the method of construct the indifferent curve.