✔ 最佳答案
The indifference is convex to the origin when total utility is increasing, marginal utility is positive. (Imagin a circle on the quadrant. Convex is the outside of the circle facing the origin.) You are still willing to sacrifice some muffins to get more pies.
When total utility decreases (marginal utiltiy becomes negative), the indifference curve is concave to the origin. (Imagin a circle on the quadrant. Convex is the outside of the circle facing opposite the origin.) You need to be paid some muffins to eat more pies.
When the indifference turns from convex to concave, the marginal utility is 0.
2007-10-15 11:30:24 補充：
At the two ends of the indifference curve, the curve is concave. In the middle part of the indifference curve, the curve is convex.
2007-10-16 00:56:54 補充：
Sorry, I think I made a mistake here.When the marginal utility of good X bceomes negative, say 3Y and 4X gives the same utility as 4Y and 5X, the indifference curve becomes upward sloping.At the two ends of IC, IC is upward sloping and in the middle, IC is downward sloping.
2007-10-16 00:57:20 補充：
Sorry for the confusion.
