Explanation:

The AFC (Average Fixed Cost) curve is the curve that is never U-shaped. Let's understand why this is the case.

Understanding the AFC curve:
The AFC curve represents the average fixed cost per unit of output. It is calculated by dividing the total fixed cost (TFC) by the quantity of output (Q). Mathematically, AFC = TFC / Q.

Characteristics of the AFC curve:
1. Always decreasing: The AFC curve continuously decreases as the quantity of output increases. This is because fixed costs are spread over a larger number of units as production increases, resulting in a lower average fixed cost per unit.

2. Asymptotic to the x-axis: The AFC curve approaches but never touches the x-axis (horizontal axis). This is because fixed costs are incurred even when there is no production (i.e., when the quantity of output is zero). Therefore, the AFC is positive for all levels of output.

Why is the AFC curve never U-shaped?
The U-shaped curve is a common characteristic of other cost curves, such as the ATC (Average Total Cost) curve and the AVC (Average Variable Cost) curve. However, the AFC curve is an exception to this pattern. It never exhibits a U-shape due to the following reasons:

1. Fixed costs do not vary with the level of output: Unlike variable costs, which change with the quantity of output produced, fixed costs remain constant regardless of the level of production. As a result, the AFC curve continuously decreases and never increases.

2. Spread of fixed costs: As more units of output are produced, the fixed costs are spread over a larger quantity, leading to a decline in average fixed costs. This spreading effect prevents the AFC curve from becoming U-shaped.

3. Fixed costs are independent of the level of output: Fixed costs are incurred even when there is no production. These costs include expenses like rent, insurance, and administrative salaries, which are not affected by the quantity of output. Therefore, the AFC curve remains positive and never becomes negative.

Conclusion:
In summary, the AFC curve is never U-shaped because fixed costs do not vary with the level of output and are spread over a larger quantity of units as production increases. This leads to a continuous decrease in average fixed costs, preventing the AFC curve from exhibiting a U-shape.