al mc 1 題 + avc mc

The antecedence variables can affect the consequence variables
可以說是因果關係

In economics, average cost is equal to total cost divided by the number of goods produced (Quantity-Q). It is also equal to the sum of average variable costs (total variable costs divided by Q) plus average fixed costs (total fixed costs divided by Q). Average costs may be dependent on the time period considered (increasing production may be expensive or impossible in the short term, for example). Average costs affect the supply curve and are a fundamental component of supply and demand.

Average cost is distinct from the price, and depends on the interaction with demand through elasticity of demand and elasticity of supply. In cases of perfect competition, price may be lower than average cost due to marginal cost pricing.

Average cost will vary in relation to the quantity produced unless fixed costs are zero and variable costs constant. A cost curve can be plotted, with cost on the y-axis and quantity on the x-axis. Marginal costs are often shown on these graphs, with marginal cost representing the cost of the last unit produced at each point; marginal costs are the first derivative of average costs.

A typical average cost curve will have a U-shape, because fixed costs are all incurred before any production takes place and marginal costs are typically increasing, because of diminishing marginal productivity. For low levels of production there are economies of scale: marginal costs are below average costs, so average costs are decreasing as quantity increases. An increasing marginal cost curve will intersect a U-shaped average cost curve at its minimum, after which point the average cost curve begins to slope upward. This is indicative of diseconomies of scale. For further increases in production beyond this minimum, marginal cost is above average costs, so average costs are increasing as quantity increases.

In economics and finance, marginal cost is the change in total cost that arises when the quantity produced changes by one unit. Mathematically, the marginal cost (MC) function is expressed as the derivative of the total cost (TC) function with respect to quantity (Q). Note that the marginal cost may change with volume, and so at each level of production, the marginal cost is the cost of the next unit produced.

A typical Marginal Cost Curve

In general terms, marginal cost at each level of production includes any additional costs required to produce the next unit.

In economics and finance, marginal cost is the change in total cost that arises when the quantity produced changes by one unit. Mathematically, the marginal cost (MC) function is expressed as the derivative of the total cost (TC) function with respect to quantity (Q). Note that the marginal cost may change with volume, and so at each level of production, the marginal cost is the cost of the next unit produced.

In general terms, marginal cost at each level of production includes any additional costs required to produce the next unit. If producing additional vehicles requires, for example, building a new factory, the marginal cost of those extra vehicles includes the cost of the new factory. In practice, the analysis is segregated into short and long-run cases, and over the longest run, all costs are marginal. At each level of production and time period being considered, marginal costs include all costs which vary with the level of production, and other costs are considered fixed costs.

AC must be higher than than MC when ac is falling because the mc means the cost of one unit of good (MC) lower than AC. 由於MC 低過AC, 所以拉低咗個平均成本, 所以此時AC下降, 但由於隨着Q 的增加, MC 會增加, 當MC高於AC時, MC會拉高平均成本(AC), 因此AC上升。
　　　　　　　　　

2007-02-02 17:22:22 補充：
AC高過MC 時, MC會拉低平均成本AC, 所以此時AC一定係FALLING隨着Q增加, MC也會增加, 當MC高於AC (即AC低於MC時), MC會拉高平均成本AC, 所以AC係RISING.所以當MC=AC時, 就是AC既MINIMUM POINT.