Final answer:
The demand function for price should establish a relationship between price and quantity demanded. While none of the given options match this strictly, the correct form would resemble P = 8 - 0.5Qd. Graphing can also be used to determine price by finding the intersection of demand and supply curves.
Step-by-step explanation:
The question asks us to identify the demand function for price. The demand function typically relates the quantity demanded (Qd) of a good to its price (P) and potentially other variables such as income or the price of other goods. In terms of mathematical representation, a standard demand function could look like Qd = a - bP, where a and b are constants with a representing the intercept and b the slope of the demand curve when graphed.
Given the options in the question, none of them strictly represents a demand function for price as the variables are not isolated and income or other product prices (pj) may be variables but are not the price of the product in question.
However, if we were to adapt these functions to describe the relationship between price and quantity demanded, we would rearrange them to solve for P, thereby obtaining a price-demand function. A correct demand function dependent on the price might look similar to the one described in the provided text: P = 8 - 0.5Qd, which suggests that the price (P) is a function of the quantity demanded (Qd).
Moreover, solving models with graphs is another approach that can be used if algebra is challenging. By graphing the demand curve, P = 8 - 0.5Qd, and the supply curve, P = -0.4 + 0.2Qs, and finding their intersection point, one can determine the market price and quantity where quantity demanded equals quantity supplied, as demonstrated in the information provided.