Final answer:
The cost curve that is a horizontal line is Total Fixed Costs (TFC). Other cost curves like ATC, AVC, and MC have different shapes: ATC and AVC are U-shaped, while MC is upward-sloping. The LRAC can show different slopes depending on economies of scale.
Step-by-step explanation:
The cost curve that is a horizontal line is Total Fixed Costs (TFC). Fixed costs do not change with the level of production, which means that the Total Fixed Cost curve remains constant or horizontal, regardless of the quantity of output.
In contrast, Average Fixed Costs (AFC) decrease as output increases, Total Variable Costs (TVC) typically have an upward slope as more output requires more variable input costs, and Total Costs (TC) also have an upward slope as they combine both fixed and variable costs.
The shapes of other cost curves are:
- Average Total Costs (ATC) and Average Variable Costs (AVC) are typically U-shaped.
- Marginal Costs (MC) are upward-sloping due to the law of diminishing marginal returns.
Lastly, the Long-Run Average Cost (LRAC) curve can be downward-sloping (economies of scale), flat (constant returns to scale), or upward-sloping (diseconomies of scale).