该题是平狄克《微观经济学》（第四）第三章复习题二。我在这找到了两种答案，不知哪能种解释是对的？

1。这种情况只能说明:对于消费者而言，这两种商品是完全相互替代的或两种商品中某一种商品是消费者所讨厌消费的。前种情况无差异曲线呈直角形；而后一种情况无差异曲线呈斜率为正。（chen1982）

2。One major assumption of preference theory is that more is preferred to less. Thus, we can expect that consumers will experience a lower level of satisfaction if we take some of a good away from them. From this, we necessarily derive negatively sloped indifference curves. However, if one good is undesirable, then less of the undesirable good leaves the consumer better off, e.g., less toxic waste is preferred to more toxic waste. When one good is undesirable, the indifference curves showing the trade-off between that good and a desired good have positive slopes. In Figure 3.2 below, the indifference curve U₂ is preferred to the indifference curve U₁.

[此贴子已经被作者于2005-2-24 10:32:22编辑过]

我想到三种情况是“不是呈负性倾斜的”：1、完全互补品（直角折线）；2、有一种商品时厌恶品（正斜率）；3、有一种商品是中性商品（垂直或水平）。

有这种情况

大家可以参考东北财经大学出版的<<微观经济学>> 汪祥春著

里面就专门标注了这个有点BT的知识点