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Find utility functions given each of the following indifference curves [defined by \(U(')=k]\) a \(z=\frac{k^{1 / 8}}{x^{a / b} y^{4 / 8}}\) b. \(y=0.5 \sqrt{x^{2}-4\left(x^{2}-k\right)}-0.5 x\) \(c_{1} z=\frac{\sqrt{y^{4}-4 x\left(x^{2} y-k\right)}}{2 x}-\frac{y^{2}}{2 x}\)

Short Answer

Expert verified
Answer: The utility functions for each indifference curve are: a) \(U(x, y, z) = \left(z x^{\alpha / \delta} y^{\beta / \delta}\right)^\delta\) b) \(U(x, y) = x^2 - \frac{1}{4}(y + 0.5 x)^2\) c) \(U(x, y, z) = x^2y - \frac{1}{4}\left(\left(2xz + y^2\right)^2 - y^4\right)\)

Step by step solution

01

Function a: Solving for utility function from the given indifference curve

Given the indifference curve: $$ z=\frac{k^{1 / \delta}}{x^{\alpha / \delta} y^{\beta / \delta}}$$ We want to find the utility function when given this indifference curve. To do so, we first need to have the equation with \(k\) representing the utility function. Rearrange the equation to make \(k\) the subject: $$k = \left(z x^{\alpha / \delta} y^{\beta / \delta}\right)^\delta$$ Now, let's denote the utility function as \(U(x, y, z)\). Then, the utility function can be expressed as: $$U(x, y, z) = \left(z x^{\alpha / \delta} y^{\beta / \delta}\right)^\delta$$
02

Function b: Solving for utility function from the given indifference curve

Given the indifference curve: $$ y=0.5 \sqrt{x^{2}-4\left(x^{2}-k\right)}-0.5 x$$ Rearrange the equation to solve for \(k\): $$k = x^2 - \frac{1}{4}(y + 0.5 x)^2$$ Now, let's denote the utility function as \(U(x, y)\). Then, the utility function can be expressed as: $$U(x, y) = x^2 - \frac{1}{4}(y + 0.5 x)^2$$
03

Function c: Solving for utility function from the given indifference curve

Given the indifference curve: $$ z=\frac{\sqrt{y^{4}-4 x\left(x^{2} y-k\right)}}{2 x}-\frac{y^{2}}{2 x}$$ Rearrange the equation to solve for \(k\): $$k = x^2y - \frac{1}{4}\left(\left(2xz + y^2\right)^2 - y^4\right)$$ Now, let's denote the utility function as \(U(x, y, z)\). Then, the utility function can be expressed as: $$U(x, y, z) = x^2y - \frac{1}{4}\left(\left(2xz + y^2\right)^2 - y^4\right)$$

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Utility Maximization
Utility maximization refers to the assumption in economics that individuals prefer to choose the combination of goods and services that provides them with the highest level of satisfaction, or utility, subject to their budget constraints. When consumers make purchasing decisions, they weigh the additional satisfaction (marginal utility) they might gain from consuming an extra unit of a good against the opportunity cost of that decision, which is typically the price of the good.

For example, in the textbook exercise, utility maximization would involve finding the combination of goods x, y, and z that maximizes the utility functions derived from the given indifference curves. Students can improve their grasp of this concept by visualizing the process as trying to find the highest indifference curve that they can reach while still remaining within their budget line. This might include activities like drawing graphs to depict the indifference curves and budget constraints, or using mathematical optimization techniques where they calculate the marginal utility per dollar spent on each good to find the optimal consumption bundle.
Consumer Theory
Consumer theory is a branch of microeconomics that studies how people decide what to purchase with their limited resources to maximize their utility. It incorporates the concept of indifference curves, which are graphs representing different combinations of two goods that provide the same level of satisfaction to the consumer. These curves help in understanding consumer preferences and are foundational in deducing demand curves.

In the given exercise, the indifference curves were described by specific functional forms, and the task was to derive the utility functions to better understand consumer choices. To better understand consumer theory, students are advised to not only focus on the algebra but to also consider the real-world implications. For example, understanding that a consumer would be indifferent between various combinations of goods x and y for a given level of utility (k) helps in realizing why consumers might substitute one good for another as prices change.
Microeconomic Models
Microeconomic models are simplified representations of real economic processes that help economists and students analyze and predict how individuals and firms will behave in a variety of circumstances. These models can range from simple supply and demand graphs to more complex mathematical models. They often use a set of assumptions to focus on specific economic variables and their interactions.

The exercise presented is an example of a microeconomic model that demonstrates how different utility functions can describe consumer behavior. In developing their microeconomic models, students could incorporate the exercise improvement suggestion by examining how changes in the parameters of the utility functions, like a, b, and k, could alter the shape of indifference curves and thus, consumer decision-making. Through this, learners gain insight into the predictive power of microeconomic models and how they can be used to understand and forecast the impact of economic changes on individual consumption choices.

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Most popular questions from this chapter

Example 3.3 shows that the \(M R S\) for the Cobb-Douglas function \\[ U(x, y)=x^{a} y^{\beta} \\] is given by \\[ M R S=\frac{\alpha}{\beta}\left(\frac{y}{x}\right) \\] a Does this result depend on whether \(\alpha+\beta=1 ?\) Does this sum have any relevance to the theory of choice? b. For commodity bundles for which \(y=x\), how does the \(M R S\) depend on the values of \(\alpha\) and \(\beta\) ? Develop an intuitive explanation of why, if \(\alpha>\beta, M R S>1 .\) Illustrate your argument with a graph. c. Suppose an individual obtains utility only from amounts of \(x\) and \(y\) that exceed minimal subsistence levels given by \(x_{0}, y_{0}\) In this case, \\[ U(x, y)=\left(x-x_{0}\right)^{a}\left(y-y_{0}\right)^{\beta} \\] Is this function homothetic? (For a further discussion, see the Extensions to Chapter \(4 .\) )

In a 1992 article David G. Luenberger introduced what he termed the benefit function as a way of incorporating some degree of cardinal measurement into utility theory." The author asks us to specify a certain elementary consumption bundle and then measure how many replications of this bundle would need to be provided to an individual to raise his or her utility level to a particular target. Suppose there are only two goods and that the utility target is given by \(U^{*}(x, y)\). Suppose also that the elementary consumption bundle is given by \(\left(x_{0}, y_{0}\right)\). Then the value of the benefit function, \(b\left(U^{*}\right)\), is that value of \(\alpha\) for which \(U\left(\alpha x_{0}, \alpha y_{0}\right)=U^{*}\) a Suppose utility is given by \(U(x, y)=x^{8} y^{1-\beta}\). Calculate the benefit function for \(x_{0}=y_{0}=1\) b. Using the utility function from part (a), calculate the benefit function for \(x_{0}=1, y_{0}=0 .\) Explain why your results differ from those in part (a). c. The benefit function can also be defined when an individual has initial endowments of the two goods. If these initial endowments are given by \(\bar{x}, \bar{y},\) then \(b\left(U^{*}, \bar{x}, \bar{y}\right)\) is given by that value of \(\alpha\) which satisfies the equation \(\left.U\left(x+\alpha x_{0}, y+\alpha y_{0}\right)=U^{*}, \text { In this situation the "benefit" can be either positive (when } U(x, y)U^{*}\right) .\) Develop a graphical description of these two possibilities, and explain how the nature of the elementary bundle may affect the benefit calculation. d. Consider two possible initial endowments, \(\bar{x}_{1}, \bar{y}_{1}\) and \(\bar{x}_{2}, \bar{y}_{2}\). Explain both graphically and intuitively why \(b\left(U^{*}, \frac{\bar{x}_{1}+\bar{x}_{2}}{2}, \frac{\bar{y}_{1}+\bar{y}_{2}}{2}\right)<0.5 b\left(U^{*}, \bar{x}_{1}, \bar{y}_{1}\right)+0.5 b\left(U^{*}, \bar{x}_{2}, \bar{y}_{2}\right) .\) (Note. This shows that the benefit function is concave in the initial endowments.

The Phillie Phanatic (PP) always eats his ballpark franks in a special way; he uses a foot-long hot dog together with precisely half a bun, 1 ounce of mustard, and 2 ounces of pickle relish. His utility is a function only of these four items, and any extra amount of a single item without the other constituents is worthless. a. What form does PP's utility function for these four goods have? b. How might we simplify matters by considering PP's utility to be a function of only one good? What is that good? c. Suppose foot-long hot dogs cost \(\$ 1.00\) each, buns cost \(\$ 0.50\) each, mustard costs \(\$ 0.05\) per ounce, and pickle relish costs S0.15 per ounce. How much does the good defined in part (b) cost? d. If the price of foot-long hot dogs increases by 50 percent (to \(\$ 1.50\) each), what is the percentage increase in the price of the good? How would a 50 percent increase in the price of a bun affect the price of the good? Why is your answer different from part (d)? f. If the government wanted to raise \(\$ 1.00\) by taxing the goods that \(\mathrm{PP}\) buys, how should it spread this tax over the four goods so as to minimize the utility cost to PP?

a. A consumer is willing to trade 3 units of \(x\) for 1 unit of \(y\) when she has 6 units of \(x\) and 5 units of \(y\). She is also willing to trade in 6 units of \(x\) for 2 units of \(y\) when she has 12 units of \(x\) and 3 units of \(y .\) She is indifferent between bundle (6,5) and bundle \((12,3) .\) What is the utility function for goods \(x\) and \(y^{3}\) Hint: What is the shape of the indifference curve? b. A consumer is willing to trade 4 units of \(x\) for 1 unit of \(y\) when she is consuming bundle \((8,1) .\) She is also willing to trade in 1 unit of \(x\) for 2 units of \(y\) when she is consuming bundle (4,4) . She is indifferent between these two bundles. Assuming that the utility function is Cobb-Douglas of the form \(U(x, y)=x^{2} y^{3},\) where \(\alpha\) and \(\beta\) are positive constants, what is the utility function for this consumer? c. Was there a redundancy of information in part (b)? If yes, how much is the minimum amount of information required in that question to derive the utility function?

As we saw in Figure \(3.5,\) one way to show convexity of indifference curves is to show that, for any two points \(\left(x_{1}, y_{1}\right)\) and \(\left(x_{2}, y_{2}\right)\) on an indifference curve that promises \(U=k\), the utility associated with the point \(\left(\frac{x_{1}+x_{2}}{2}, \frac{y_{1}+y_{2}}{2}\right)\) is at least as great as \(k\). Use this approach to discuss the convexity of the indifference curves for the following three functions. Be sure to graph your results. a. \(U(x, y)=\min (x, y)\) b. \(U(x, y)=\max (x, y)\) c. \(U(x, y)=x+y\)

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